Explosion-proof motors – explosion protection device
Explosion-proof motors.
Fire temperature – heat resistance class.
The fire temperature depends on various factors such as size, shape, type and composition
surfaces. In IEC (IEC) 79-4 standards, and CENELEC (European Committee for Electrotechnical Engineering
standards) a “procedure for determining the temperature of ignition” is defined with a limit approaching
to the lowest possible value.
Gases and vapours are divided into heat resistance classes. According to heat resistance classes
electrical equipment is tested for maximum surface temperature in order to
exclude the possibility of fire due to surface temperature, both during normal operation, and
and in the event of a malfunction. These standards specify the extent to which standard values can be exceeded
and the necessary safety limits are defined.
| Class heat resistance |
Temperature range mixture ignition |
Allowable temperature surfaces electrical equipment |
Permissible uplift temperatures |
| T1 | > + 450 °C | + 450 °C | + 410 °C |
| T2 | > + 300… ≤ + 450 °C | + 300 °C | + 260 °C |
| T3 | > + 200… ≤ + 300 °C | + 200 °C | + 160 °C |
| T4 | > + 135… ≤ + 200 °C | + 135 °C | + 95 °C |
| T5 | > + 100… ≤ + 135 °C | + 100 °C | + 60 °C |
| T6 | > + 85… ≤ + 100 °C | + 85 °C | + 45 °C |
Examples of division of gases and vapours into heat resistance classes and explosion protection subgroups
| T1 | T2 | T3 | T4 | T5 | T6 | |
| IIA | Methane | Propane | Petrol | Acetaldehyde | ||
| IIB | Ethylene | Diethyl ether |
||||
| IIC | Hydrogen | Acetylene | Carbon sulphide |
Providing protection against explosion during operation.
Electrically driven machines must be protected against overheating caused by overloading.
The type of protection depends on the type of work and on the type of electrically driven machine and its application.
Explosion-proof electric motors are usually certified for operation type S1, i.e.
uninterrupted. Other modes are only allowed if reliable monitoring devices are used
of the engine temperature.
| Operating mode | Safety control device |
| S1* | A Motor emergency switch according to IEC 34-1 (VDE 0165/9.83) |
| B Motor emergency switch and winding temperature sensors as additional protection | |
| C Only temperature sensors as the main defence. Only authorised if the motor has been tested and certified and if all control devices used (power supplies) have passed certification |
|
| S2/S3* | D Motor emergency stop switch with adjustable switch-on time and/or temperature sensors in the winding as additional protection |
| E Temperature sensors as a basic defence. Permitted only if The engine has been tested and certified, and all devices used controls (power supplies) have been certified |
|
| S4, S5, S6, S7, S8* | F Winding temperature sensors. The motor must be tested and only certified control devices may be used. |
| Powered by converter frequencies |
G The thermal protection of the motor by means of sensors in the winding can only be the only (independent) protection if the motor is tested at all power supply frequencies, maximum voltages and operating modes S1-S7 (S8). |
| H If motor protection and transformer have been tested and certified together |
* Description of operating cycles.
Operating cycles
S1 Prolonged work
Operation with a constant load continues long enough for the machine to reach temperature equilibrium.
Symbol: S1
S2 Short-term operation
Operation with a constant load for a period of time insufficient for the machine to reach temperature equilibrium. The machine is idle long enough for the machine to cool down to ambient temperature.
Standard duration of short-term operation: 10, 30, 60 and 90 minutes.
Symbol: S2 30 minutes
S3 Repetitive-periodic operation mode
Operation in defined cycles under repeated constant load. The operating and idle periods are too short for the motor to reach temperature equilibrium. Start-up losses are small and have no significant effect on the temperature increase. Relative start-up time ratings of 15, 25, 40, 60 % on a daily 10-minute cycle.
Symbol: S3 25 %
S4 Repetitive-periodic operation mode
Operation in defined cycles under repeated constant load. Starting the engine affects the temperature rise.
To determine this type of mode, it is necessary to know the number of cycles (starts per hour) and the inertia factor.
Symbol: S4 40 %; 120 starts/h; FI2
S5 Repetitive-periodic operation mode
Similar to S4, except that the electrical braking of the machine has a significant effect on the temperature increase.
Symbol: S5 160 %; 120 starts/h; FI2
S6 Prolonged work with cyclic loading
The work consists of a long series of equal cycles. Each cycle includes a no-load period and a steady load period.
The cycle does not continue long enough for the machine to reach temperature equilibrium in one cycle.To define the S6 mode, the relative start time must be specified.
Symbol: S6 15 %
S7 Repetitive-periodic operation with start-up and braking
Continuous operation with a series of constant load and deceleration periods. The toughest mode of engine operation. To determine this mode of operation, the number of cycles per hour and the coefficient of inertia must be specified.
Symbol: S7 500 starts/h; FI3
S8 Repetitive-periodic operation with pole switching
This mode of operation is only available for motors with modulated pole amplitude. In this case, the mode definition must contain the following data for each pole:
– number of starts per hour
– inertia coefficient
– relative work period
Symbol: S8 30 starts/h; FI10; 740 rpm; 40 %
S8 30 starts/h; FI10; 960 rpm; 60 %
Explosion-proof motors.
Fire temperature – heat resistance class.
The fire temperature depends on various factors such as size, shape, type and composition
surfaces. In IEC (IEC) 79-4 standards, and CENELEC (European Committee for Electrotechnical Engineering
standards) a “procedure for determining the temperature of ignition” is defined with a limit approaching
to the lowest possible value.
Gases and vapours are divided into heat resistance classes. According to heat resistance classes
electrical equipment is tested for maximum surface temperature in order to
exclude the possibility of fire due to surface temperature, both during normal operation, and
and in the event of a malfunction. These standards specify the extent to which standard values can be exceeded
and the necessary safety limits are defined.
| Class heat resistance |
Temperature range mixture ignition |
Allowable temperature surfaces electrical equipment |
Permissible uplift temperatures |
| T1 | > + 450 °C | + 450 °C | + 410 °C |
| T2 | > + 300… ≤ + 450 °C | + 300 °C | + 260 °C |
| T3 | > + 200… ≤ + 300 °C | + 200 °C | + 160 °C |
| T4 | > + 135… ≤ + 200 °C | + 135 °C | + 95 °C |
| T5 | > + 100… ≤ + 135 °C | + 100 °C | + 60 °C |
| T6 | > + 85… ≤ + 100 °C | + 85 °C | + 45 °C |
Examples of division of gases and vapours into heat resistance classes and explosion protection subgroups
| T1 | T2 | T3 | T4 | T5 | T6 | |
| IIA | Methane | Propane | Petrol | Acetaldehyde | ||
| IIB | Ethylene | Diethyl ether |
||||
| IIC | Hydrogen | Acetylene | Carbon sulphide |
Providing protection against explosion during operation.
Electrically driven machines must be protected against overheating caused by overloading.
The type of protection depends on the type of work and on the type of electrically driven machine and its application.
Explosion-proof electric motors are usually certified for operation type S1, i.e.
uninterrupted. Other modes are only allowed if reliable monitoring devices are used
of the engine temperature.
| Operating mode | Safety control device |
| S1* | A Motor emergency switch according to IEC 34-1 (VDE 0165/9.83) |
| B Motor emergency switch and winding temperature sensors as additional protection | |
| C Only temperature sensors as the main defence. Only authorised if the motor has been tested and certified and if all control devices used (power supplies) have passed certification |
|
| S2/S3* | D Motor emergency stop switch with adjustable switch-on time and/or temperature sensors in the winding as additional protection |
| E Temperature sensors as a basic defence. Permitted only if The engine has been tested and certified, and all devices used controls (power supplies) have been certified |
|
| S4, S5, S6, S7, S8* | F Winding temperature sensors. The motor must be tested and only certified control devices may be used. |
| Powered by converter frequencies |
G The thermal protection of the motor by means of sensors in the winding can only be the only (independent) protection if the motor is tested at all power supply frequencies, maximum voltages and operating modes S1-S7 (S8). |
| H If motor protection and transformer have been tested and certified together |
* Description of operating cycles.
Operating cycles
S1 Prolonged work
Operation with a constant load continues long enough for the machine to reach temperature equilibrium.
Symbol: S1
S2 Short-term operation
Operation with a constant load for a period of time insufficient for the machine to reach temperature equilibrium. The machine is idle long enough for the machine to cool down to ambient temperature.
Standard duration of short-term operation: 10, 30, 60 and 90 minutes.
Symbol: S2 30 minutes
S3 Repetitive-periodic operation mode
Operation in defined cycles under repeated constant load. The operating and idle periods are too short for the motor to reach temperature equilibrium. Start-up losses are small and have no significant effect on the temperature increase. Relative start-up time ratings of 15, 25, 40, 60 % on a daily 10-minute cycle.
Symbol: S3 25 %
S4 Repetitive-periodic operation mode
Operation in defined cycles under repeated constant load. Starting the engine affects the temperature rise.
To determine this type of mode, it is necessary to know the number of cycles (starts per hour) and the inertia factor.
Symbol: S4 40 %; 120 starts/h; FI2
S5 Repetitive-periodic operation mode
Similar to S4, except that the electrical braking of the machine has a significant effect on the temperature increase.
Symbol: S5 160 %; 120 starts/h; FI2
S6 Prolonged work with cyclic loading
The work consists of a long series of equal cycles. Each cycle includes a no-load period and a steady load period.
The cycle does not continue long enough for the machine to reach temperature equilibrium in one cycle.To define the S6 mode, the relative start time must be specified.
Symbol: S6 15 %
S7 Repetitive-periodic operation with start-up and braking
Continuous operation with a series of constant load and deceleration periods. The toughest mode of engine operation. To determine this mode of operation, the number of cycles per hour and the coefficient of inertia must be specified.
Symbol: S7 500 starts/h; FI3
S8 Repetitive-periodic operation with pole switching
This mode of operation is only available for motors with modulated pole amplitude. In this case, the mode definition must contain the following data for each pole:
– number of starts per hour
– inertia coefficient
– relative work period
Symbol: S8 30 starts/h; FI10; 740 rpm; 40 %
S8 30 starts/h; FI10; 960 rpm; 60 %
