GB 5959.3-1988 Safety of Electric Heating Equipment Part 3 Special Requirements for Induction and Conductive Heating Equipment and Induction Melting Equipment
Some standard content:
National Standards of the People's Republic of China
Safety in electroheat installations
Part 3: Particular requirements for induction and conductive heating equipment and induction melting equipment
Safety in electroheat installationsPart 3: Particular requirements for induction and conduction heating installations and induction melting installationsGB5959.3-88
This standard is equivalent to the international standard IEC519-3 "Safety of Electric Heating Equipment Part 3 Special Requirements for Induction and Conductive Heating Equipment and Induction Melting Equipment".
1 Subject content and scope of application
1.1 This standard, in conjunction with GB5959.1, stipulates: a. General safety requirements for induction and conductive heating equipment and induction melting equipment; b. Special safety requirements for two types of equipment: Part A and Part B 1.2 This standard applies to:
a. Equipment for induction and conductive heating of solid charge at industrial, medium and high frequencies (conductive heating is also Including DC electric heating); b. Equipment for induction melting, insulation and liquid charge heating at working, medium and high frequencies; c. Parts of the transmission device or loading and unloading mechanism on the electric heating equipment that are affected by the heating part. Application examples:
Induction and conductive heating equipment for heating plates, flat ingots, bars, strips, wires, pipes, rivets, etc. for thermoforming and heat treatment;
Centerless induction Furnace or induction furnace equipment. 2 Reference standards
GB2900.23 Electrical terms and terms Industrial electric heating equipment GB5959.1 Safety of electric heating equipment Part 1 General requirements GB4064 Safety design guidelines for electrical equipment
GB4824.1 Industrial, scientific and medical radio frequency equipment Radio interference allowable value 3 terms
Except for the following terms, for the definitions of terms used in this standard, please refer to Chapter 2 "Terms" of GB2900.23 and GB5959.1. 3.1 Induction heating
Heating method that generates heat energy in the charge by electromagnetic induced eddy current. 3.2 Conductive heating (direct resistance heating)
The current flows directly through the heated charge to produce heating. This current is not caused by electromagnetic induction. The Ministry of Mechanical and Electronics Industry of the People's Republic of China approved the implementation on 1989-07-01 on 1988-08-31
3.3 Heating part
GB5959.3-88
Induction heating or conductive heating in the device part. 3.4 Contact system
is a component of the conductive heating workbench, through which the charge is electrically connected to the heating power source. 4 Sensor
4.1 Depending on the usage or to meet new production requirements, the sensor or its components should be able to be easily replaced according to the manufacturer's instructions. 4.2 The coolant temperature of the sensor should be prevented from falling below the dew point, as this may cause condensation on the coil and its terminals, resulting in a short circuit. 4.3 The voltage applied to the inductor (such as a coil with a tap) should not exceed the value specified by the manufacturer. 5 Capacitors
5.1 Necessary measures should be taken to quickly discharge capacitors that may come into contact after a power outage. A warning sign should be placed in a prominent location stating that capacitors must be discharged before touching them.
5.2 For capacitors permanently connected in parallel to the working coil of the inductor or the transformer, the discharge device can be omitted. When the capacitor connected in parallel to the inductor or transformer can only be disconnected during a power outage, the discharge device can also be omitted, but it is required that there should be sufficient delay after the power outage to fully discharge the capacitor before cutting off the capacitor. Note: If DC charging is possible, discharging and reloading is essential. 5.3 Capacitors operated under load or connected through external fuses should be equipped with a discharge device. 5.4 The discharge device should be dedicated. It cannot be used for short circuiting between capacitor terminals, nor can it be used as a grounding device before contacting the capacitor.
Note: Although the discharge device is working, the common connection of the series capacitors may be damaged due to blown fuses, broken internal connections, differences in capacitance values, or dielectric recharging caused by DC components during previous charging. Sometimes residual charges are generated. 5.5 Low-frequency capacitors should be connected through protective devices. When an internal fuse is used, no external protection device is required. Capacitors for medium and high frequencies may not be connected via protective devices.
5.6 For liquid-cooled capacitors, the coolant temperature should be monitored with an automatic alarm device. If the cooling system of several capacitors is connected in series, the temperature of the coolant at the outlet of the last capacitor needs to be monitored. For capacitors that are switched on or off respectively, the last capacitor connected in series in the cooling circuit shall be the one permanently connected to the circuit or the last one to be de-energized. 5.7 The monitoring of capacitor temperature can be replaced by monitoring the temperature of the coolant at the outlet or monitoring the flow rate of each cooling circuit. 6 Industrial frequency power supply
For industrial frequency power supply that supplies power to single-phase loads from a three-phase power supply and uses capacitors and reactors to achieve three-phase current balance, if it is connected to the common point of the capacitors and reactors of the balancing circuit If the phase is open (for example, the fuse is blown or the contactor on the line is faulty), series resonance will occur and cause safety-threatening overvoltage. In this case, measures should be taken to cut off the power supply, such as using the overvoltage trip of the power circuit breaker. The contactor that controls the three-phase power supply to the reactor-capacitor balancing circuit should be designed to ensure that the contacts connected to the common point of the reactor and capacitor should be closed early when closing, and should be opened delayed when tripping. 7 Motor generator type variable frequency unit (frequency converter) 7.1 The heating device and frequency converter should be able to withstand the instantaneous overvoltage that may occur when the power is rapidly reduced or the capacitor is closed. 7.2 The excitation current can only be applied after the frequency converter has reached its normal operating speed and the starting procedure has been completed. 7.3 The frequency converter should be equipped with overcurrent and overvoltage protection devices, which should include time-related components that match the transient thermal characteristics of the frequency converter. Due to the large inertia of thermal protection devices, they are usually not used. 7.4 If there is a voltage surge that is not allowed even for a short period of time, a direct-acting protective device should be used, such as a surge arrester. GB5959.3-—88
Series compensated frequency converters should have appropriate protection devices, such as series capacitor short-circuit devices. 7.5 When the frequency converter does not have an automatic voltage control device, it is only allowed to connect the capacitor or reduce the power through switching operation when the output voltage of the frequency converter is at a safe value.
8 Electronic frequency conversion device (frequency conversion device)
8.1 The frequency conversion device should be protected at the input end to prevent instantaneous overvoltage that may occur during power side switch operation to ensure safety. 8.2 Frequency conversion devices should have fast-acting overvoltage and overcurrent protection. 8.3 Additional measures should be taken to prevent dangerous instantaneous overvoltage due to rapid changes in load power. 9 Ferromagnetic frequency doubler
9.1 The ferromagnetic frequency doubler referred to in this standard is a general three-phase/single-phase type. The frequency multiplier consists of a specially connected single-phase reactor (i.e. current coil or transformer) with a highly magnetically saturated core. Cooling, control and safety should comply with transformer standards. 9.2 Capacitors and reactors should be connected to the three-phase input ends of the frequency multiplier to compensate for the high magnetizing current of the frequency multiplier reactor and limit the harmonic current in the power supply network.
10 Switching device
10.1 When designing the on-load switching device of the frequency converter, the voltage characteristics of the inverter when the load suddenly decreases should be considered. 10.2 When designing the off-load switching device, the variable frequency power supply should be considered , time characteristics of reactive components (transformers and reactors) and capacitors, 10.3 The design of switching devices must not only consider the fundamental component of the current, but also consider the harmonic components that may be generated by the equipment. 10.4 When the on-load switching capacitor is used, the following points should be considered in the selection of switching device or switching mode: a. When closing, a high current peak may be generated on the high-frequency side: b. When opening, the overvoltage caused by the arc of the switching device should be avoided from reaching dangerous values. 11 Cables, wires and busbars
11.1 The specifications and dimensions of cables, wires and busbars should be such that the temperature of their own heating does not exceed their allowable values ??under the current load and frequency carried.
Note: Current values ??suitable for power frequency (50Hz or 60Hz) are generally not suitable for higher frequency equipment. In the case of parallel connections, care should be taken to avoid overheating of individual conductors due to uneven current distribution. 11.2 If forced cooling is used for power lines, wires or busbars, the relevant provisions of Articles 4.2.8, 4.6.1 and 4.6.2 in GB5959.1 should be followed.
11.3. Internal connections to components such as ferromagnetic frequency multipliers, electronic frequency converters, transformers, capacitors, switching devices, inductors and contact systems may not be required if these connections do not cause short circuits and are not electrically thin. Separate overcurrent protection device. Note: If cables, rigid conductors, and single-core conductors are spaced apart from each other or use insulating gaskets, or the conductors are arranged in their own insulated conduits, or cables or wires are designed to provide short-circuit protection, this will This prevents contact between these wires (including grounded parts). For medium frequency or high frequency equipment, if the designed variable frequency power supply (such as electronic frequency conversion device) can provide reliable short circuit protection, it is not necessary to take the above measures to strengthen short circuit protection.
11.4 Cables and conductors in heated areas should generally have an insulation layer of high mechanical and thermal strength. In most cases, this insulation layer is not sufficient as a protective measure against electric shock. If the permissible contact voltage is exceeded, measures should be taken to prevent accidental contact with these cables and conductors during operation.
12 Liquid cooling
For requirements on liquid cooling, please refer to GB5959.1 Article 4.6. GB5959.3-88
12.1 For high-frequency devices operating in the third voltage range, the formation of bubbles in the cooling system should be avoided, because arcs may be generated in the bubbles and damage the cooling system.
Note: For the classification of voltage sections, please refer to GB5959.1 Article 3.1. 12.2 For hoses reinforced with fabric, moisture may penetrate along the fabric reinforcement, thereby generating a potential difference between the reinforcement and the coolant. This potential difference may exceed the electrical insulation strength of the pipe wall. Therefore, this should be taken into consideration when selecting hose materials and layout. 12.3 Some liquid-cooled components (such as ceramic capacitors and liquid-cooled casings of electron tubes) are very sensitive to the pressure of the coolant. Therefore, the requirements of Article 4.6.4 in GB5959.1 do not apply to them. These liquid cooling components can only withstand the rated working pressure, and their joints should withstand 1.5 times the rated working pressure. 12.4 For liquid cooling components such as inductors, capacitors, switching devices, transmission devices, contact system liquid cooling systems, fire transformers, high-power thyristors, oscillation tubes, etc., the protection of liquid pressure, liquid temperature, and flow rate should be considered during design. Of course, these liquid cooling systems are not allowed to have fluid outages. A backup coolant source should be considered to provide cooling for various components in the event of a sudden fluid outage. The backup fluid volume should be able to last until the cooled components reach a safe temperature.
13 Nameplate
13.1 For the nameplate of electric heating equipment, please refer to Chapter 6 of GB5959.1. 13.2 Each main component of the electric heating equipment (for example: sensor, contact system) should be equipped with its own nameplate if necessary. 14 Electrical clearance and creepage distance
For the electrical clearance and creepage distance of high-frequency and medium-frequency equipment, it is not necessary to adopt the values ??used at power frequency (50Hz/60Hz). When smaller values ??are used (e.g. in high-frequency generators), measures should be taken to prevent safety-threatening flashovers. The specific values ??of electrical clearances and creepage distances should be specified in product standards. 15 Electric shock protection
15.1 Direct contact protection
The direct contact protection measures taken should meet the requirements of Article 4.9.1.2 of GB4064. 15.1.1 The relationship between allowable contact voltage and frequency. The limit value of allowable contact voltage is a function of frequency, and the value increases with frequency. When determining the permissible contact voltage from the existing limit values ??for the power frequency, DC and second voltage ranges given in the table and figure below, it should be taken into account that the permissible contact voltage increases with frequency. Maximum contact voltage duration schedule
Maximum cut-off time t
s
8
5
1
0.5
0.2
0.1
0.05
0. 03
AC
(rms value)
<50
50| |tt||75
90
110
150
220
280
Expected contact voltage U, V||tt| |DC
<120
120
140
160
175
200
250
310
Note: ①The DC column in the table applies to non-pulsating DC, such as when powered by a battery. For rectified power supplies powered by AC, the AC values ??may be used. ②The waveform of the expected contact voltage on the DC equipment may be different from the waveform of the system voltage, which depends on the parameters of the fault circuit. t (s)
8.0
6.0
4.0
2.
1.
0.80
0.60|| tt||0.40
0.20
0.10
0.00
0.04
0.02
GB5959.3—88
dc
20304050,60801002003001005001000 Duration corresponding to the maximum contact voltage in the table 15.1.2 All electrical components of the heating equipment, such as capacitors, reactors, transformers, inductors or contact systems, switching devices, cables and busbar connections etc., should be installed in a cabinet, otherwise adequate protection should be provided to avoid direct contact. For devices operating in the second and third voltage ranges, they should be designed so that only special tools (such as wrenches) or trained personnel and specially designated persons can open the cabinet door and remove the outer cover. Get close to these parts. 15.1.3 Access to live conductors operating in the second and third voltage sections shall not be allowed unless the following conditions are met: for the second voltage section, only specially trained personnel and designated persons may approach; for the third voltage section, Three-voltage zones shall be designed to prevent accidental contact with live conductors by designated personnel during troubleshooting, testing or maintenance. The following measures can be taken:
a. For covers fixed with screws, they can only be accessed after the power is turned off; b. For the use of lockable hinged swing doors or hinged swing inner shields, a reliable, non-resettable safety switch should be installed to ensure that the door is closed before the power is turned on again, and connectors of appropriate specifications should be led out for external connections. For test instruments; c. Where internal shields and barriers are used, an internally fixed shield or barrier shall be used to cover the location of the voltage test point. The shield shall have openings or gaps sized to allow only the insertion of the test probes. 15.1.4 Accessible AC, DC or high-frequency plugs and sockets with voltages higher than 500V should not be interchangeable; and the power supply must be turned off before or at the moment when the plugs and sockets are disconnected. So as not to endanger personal safety. 15.2 Indirect contact protection
According to the needs of the type of electric heating equipment or operating conditions, in order to prevent operators from being exposed to the risk of electric shock in the event of an accident, the following conditions are allowed as a supplementary condition to the regulations on indirect contact protection. This condition is that the rated voltage of the electric heating equipment does not exceed the second voltage range, and other protective measures have been taken, such as wearing insulating clothing, insulating gloves, insulating shoes, protective caps and goggles and other personal protective equipment, and setting up insulating platforms and Use insulated or grounded tools, etc. GB5959.388 | changes throughout the work cycle. Generally the minimum insulation resistance value is not given. Therefore, when the equipment is delivered for production, these changes must be considered when setting the action value of the protection device (such as the ground leakage current detection device). wwW.bzxz.Net
The relationship between the allowable contact voltage and frequency in the case of continuous contact is the same as that in the case of direct contact. Since induction heating equipment has considerable leakage current, the electric heating equipment and the power supply should be electrically isolated when necessary. 15.3 Special Requirements
No person should wear items such as metal rings and bracelets near medium-frequency and high-frequency strong electromagnetic fields (such as near sensors). 15.4 Ground protection
15.4.1 If in a piece of equipment that is electrically isolated from the power supply, live parts are connected to the earth through a resistor, impedance or limiter, the size of the earth wire shall take into account the thermal effects and electrodynamic forces at the maximum current generated in the event of a fault and shall be Monitor the current in these ground connection wires. If the maximum allowable value is exceeded during operation, an alarm signal should be given and the power supply of the equipment should be automatically turned off. The above-mentioned monitoring is not required for connecting lines used for electrostatic discharge or similar situations and for connecting lines of high-frequency equipment that have protective facilities for the inductors and that can stop the operation of the heating device as soon as the protective facilities are removed. 15.4.2 When earth fault protection is used, the relationship between frequency and the impedance of the circuit formed by the power supply, current-carrying conductors and the earth system should be considered. 15.4.3 For metal parts that are not grounded and are directly affected by electromagnetic fields, in order to avoid the formation of closed metal loops and limit electromagnetic and thermal effects within the allowable range, other protective measures should be taken based on operational needs. For parts whose working voltage exceeds the allowable contact voltage, it should be impossible for operators to approach it. If contact with these parts is unavoidable because the space is too small or due to the way the equipment is operated, other protective measures should be given to ensure personal safety and described in the instructions.
15.4.4 All armored cables, conduits or tubes passing through cabinets containing high-voltage circuits in the third voltage zone shall be earthed at the point where they pass through the cabinet.
15.4.5 If the overload monitoring of the power transformer can immediately cut off the high-voltage circuit, the grounding protection of the power supply system in the second voltage section can be used for the circuit in the third voltage section of the high-frequency generator. Measures note: Usually, the power distribution system in the third voltage section is required to be separately grounded, but since the short-circuit power of the high-frequency circuit of the generator itself is small, separate grounding is not necessary.
15.5 Protective conductor
The material of the protective conductor for power frequency devices is copper, aluminum or galvanized steel strip; while medium frequency or high frequency devices should use copper or aluminum. The discharge current of the capacitor should also be taken into account when determining the size of the conductor cross-section. The depth of current penetration decreases with increasing frequency and this factor should be taken into account when considering the cross-sectional dimensions of the protective conductors. 16 Radio interference
When electric heating equipment is running, radio interference must be suppressed in accordance with the requirements of GB4824.1. A1 conveyor and charge
GB5959.3-88
Appendix A
Special requirements for induction and conductive heating equipment (supplement)
A1.1 conveyor It should be able to withstand the influence of temperature from the heated material. The design of conveying devices should take into account the effects of electromagnetic fields. In addition to the selection of appropriate materials and geometries, further measures (such as shielding, isolation, prevention of metallic closed loops and forced cooling) are necessary to keep electromagnetic and thermal influences within permissible limits. The influence of the electromagnetic force acting on the charge should also be considered during design. A1.2 The design of the conveyor device should meet the changes in volume and mechanical strength of the charge during the heating process. A1.3 Materials whose size, shape, physical properties, burrs and tolerances must be agreed upon by the user and the manufacturer should be used to ensure that Safe production and accurate working procedures of heating equipment.
A1.4 Since different materials have different physical phenomena, it is impossible to accurately estimate the temperature distribution in the charge through the measurement of surface temperature. Therefore, the possibility of overheating of the charge cannot be ruled out, and attention should be paid to reducing this localization. The danger of overheating. The existence of A1.5 metal residue, that is, oxide scale, may affect the pushing of the charge and the reliability and safe production of the heating equipment. These oxide scales and residues should be removed according to the requirements of the manufacturer's instructions. A1.6 For transmission devices or their components that use forced cooling (such as water cooling), refer to Article 12.4. A2 contact system
A2.1 The contact system or its components should be easily replaceable in accordance with the manufacturer's instructions. A2.2 During closing of the heating power supply, a suitable hood should be used to maintain the contact pressure value given by the manufacturer. For example, a locking system that uses a power-only release mechanism to open and simultaneously disconnect the heating power supply. A2.3 During normal operation, the contacts should be closed or opened only when the heating power supply is disconnected to prevent arcs and voltage shocks. Measures should be taken to prevent the sputtering of hot metal particles from endangering the safety of people and equipment. . A2.4 In the case of rapid transfer of charge (such as tube material), measures should be taken to prevent damage to contact systems or their clamping mechanisms due to surface irregularities. For example, these charges can be shaped and transferred through necessary channels. A2.5 When the contact system is without electrical insulation and operates above the allowable contact voltage value, the device should be designed to make it impossible to accidentally contact the exposed contact system under normal use conditions, such as using protective shielding or Separate enough distance to achieve this. Where it is impossible to set up protective shielding or other protective measures, a warning signal should be set on the equipment and should comply with GB5959.1 Article 10.2.
A2.6 When the cooling effect of the contact system is insufficient and thus endangers personal safety or major components of the device, an alarm signal should be given and the heating power supply should be automatically cut off. || tt | When the voltage value is high, the protection measures should be in accordance with A2.5. A4 Special requirements (see Article 15.3)
Induction heating devices used in the manufacture, processing or repair of pipes, vessels or boilers are usually only allowed to operate at the voltage of the first voltage zone, if necessary. , can also be used in the second voltage section, but the following precautions should be taken: a. Use a frequency converter or a transformer with separate windings and extremely high insulation withstand voltage strength and high insulation resistance to ground; GB5959.3-88
Use equipotential connection to provide a safe contact for the operator area, otherwise use insulated gloves and insulated shoes. The b.
circuit shall not have a ground point unless passed through an insulation monitoring system. If direct or indirect contact is unavoidable with live parts (such as water-cooled heating cables) whose insulation is not good at preventing electric shock, insulating protective equipment or insulating tools must be used. A5 Ground protection (see Article 15.4)
In cases where the charge or moving parts of the conveyor system cannot usually be fixedly grounded or connected to a protection system, other protective measures should be taken in accordance with Article 15.2.
Appendix B
Special requirements for induction melting equipment
(supplement)
B1 tilting device
When the furnace is equipped with a tilting mechanism , should meet the following requirements: B1.1 When the furnace tilting mechanism fails, the furnace should stay in the position reached or slowly return to the normal position, and there should not be any danger when resetting.
B1.2 If during furnace tipping there is a risk of workers falling into a pit normally covered by the furnace platform, measures should be taken to prevent this. These measures should not create other hazards such as shearing or crushing. B1.3 In the case of hydraulic tilting furnace, the pump, working fluid storage tank and pipelines should be reasonably arranged to prevent accidental accidents caused by accidental splashing of molten metal.
B1.4 The tilting action of the furnace should be limited in both directions. B1.5 If the live parts are easily accessible when tilting the furnace, the furnace must be tilted when the power is cut off. If the power cut is not allowed, There should be protective measures.
B1.6 The starting lever of the hydraulic furnace tilting device should be able to return to the zero position automatically. B1.7 For any tilting device, buttons and joysticks shall be non-retentive in the on position. B1.8 The hydraulic device used must ensure the smoothness of the furnace tilting action and the reliability of operation. B1.9 There should be an emergency furnace tilting mechanism to tilt the furnace in an emergency (such as a sudden power outage) to save the furnace. B2 Furnace Basics
B2.1 There should be a storage pit or ladle pit that can contain all molten metal in the event of emergency furnace tipping or leakage. The pit should be protected by a fence or cover.
B2.2 The design of the area below the furnace should ensure that molten metal can quickly flow into the storage pit in front of the furnace in the event of a furnace leakage failure to prevent damage to the furnace and other parts of the equipment.
B2.3 There should be no accumulation of water in the storage pit or ladle pit or under the furnace, because there is a risk of explosion of molten metal when it comes into contact with water. B3 Furnace Village
Molten metal penetrating the furnace lining will cause furnace leakage that is dangerous to people and equipment, so the condition of the furnace lining should be checked regularly. Specific methods B3.1
:
a.
Measure the electrical parameters of the equipment;
b.
Visual inspection;
c.
Measure crucible diameter at different heights (centerless furnace); GB5959.3-88
d, temperature detection (coolant temperature of sensor shell and cored furnace) B3.2. For the safety of the operator and to reduce the risk of furnace damage, when the electrical insulation of the furnace lining is damaged below a certain critical value and leakage of the furnace lining may occur, an alarm signal should be issued and the power supply should be automatically cut off. B4 Operation
B4.1 The following factors should be controlled to prevent the molten metal from overheating and burning: a. Control input power
b. Reasonable addition of ingredients.
B4.2 The charge should be added to the molten pool according to the smelting process to keep its temperature within the allowable range. B4:3 The charging process should not cause the surface of the molten metal to solidify or cause the charge above the molten pool to fuse together. (Building a bridge). B4.4 In order to prevent overheating, the temperature of the molten metal should be measured according to the product instructions. B4.5 There should be strict requirements for the charge and pre-drying measures must be taken. If the charge added to the molten pool has a cavity, which may contain moisture, special precautions should be taken to prevent molten metal from entering and exiting, which may cause danger. B4.6 Appropriate devices should be used to eliminate toxic fumes or other gases that may be generated during smelting. Danger. B5 Grounding Protection
The charge cannot be grounded as firmly as some easily accessible metal parts. Therefore, other protection measures should be taken according to Article 15.2, and the insulation monitoring system of B3.2 is recommended. B6 Thermal Protection
Corresponding protective measures should be taken against the high temperature of the melting furnace, the sputtering of the molten charge, etc. to ensure the safety of operators. Additional notes:
This standard is proposed and coordinated by the National Industrial Electric Heating Equipment Standardization Technical Committee. This standard is drafted by Xi'an Electric Furnace Research Institute.
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