The SIMOREG CCP (Converter Commutation Protector) is used to protect a line commutated SIMOREG 6RA70 DC MASTER from the effects of inverter commutation failures.
For line-commutated converters in order to commutate the current between the individual power semiconductors, an appropriate line-side counter voltage is required. As a result of uncontrolled switching operations caused by line supply interruptions/dips (e.g. weak line supplies, thunderstorms, etc.), the completion of commutation can be prevented (inverter commutation failures). A large current is created in the regenerating direction via the power system or a crossover current is created in the power converter. This can result, in turn, to ruptured fuses or under certain circumstances, to destroyed power semiconductors.
By expanding the basic software of the SIMOREG DC MASTER, an inverter commutation failure is quickly detected and a command is then issued to the SIMOREG CCP to turn-off the power semiconductors in the basic unit. The SIMOREG CCP turns-off the power semiconductors, ensures that the right conditions are available to reduce the current in the motor and absorbs the magnetic energy, stored in the motor, as electrical energy.
The SIMOREG CCP limits the current created with inverter commutation fault to a harmless level so that thyristors and the associated super-fast fuses are protected. As a result, timeconsuming and expensive replacement of the fuses is no longer necessary
The inverter commutation failure cannot be prevented but its effects can. • Any gear units used are protected against inadmissibly high torque surges in the event of a fault by de-energizing the current in good time before the maximum current value is reached.
• Up till now high-speed DC circuit-breakers have already been used to protect against blown fuses in the event of high system rated currents. The use of the CCP now provides cost-effective protection even in the case of smaller rated currents; the SIMOREG CCP offers the following advantages compared to highspeed DC circuit-breakers:
– Protection even in the case of circulating current – Lower system costs – Lower space requirement – No additional air reactors necessary to reduce current gradients in the event of a fault – Lower operating costs due to being maintenance-free – Higher availability
Design and Working principle
SIMOREG CCP is distinguished by its compact and space-saving design. The line voltage, the line current, and the armature voltage are recorded in the basic unit. These quantities are used to determine whether a commutation failure has occurred (“conduction-through”).
If this is the case, the following happens: 1. The firing pulses in the SIMOREG DC MASTER are blocked immediately 2. The SIMOREG DC MASTER transmits (via serial interface) an “extinguish command” to the SIMOREG CCP
3. The SIMOREG CCP extinguishes the thyristors by connecting precharged extinguishing capacitors antiparallel to all thyristors. Consequently, the current commutates from the converter into the SIMOREG CCP. The surge absorbing capacitors will initially be discharged by the accepted current and then charged reversed. Once the voltage of the surge absorbing capacitors has reached the value of the motor EMF, the armature current begins to extinguish itself. The armature voltage, however, continues to increase. As soon as it has attained the limiting value, resistors will be added that accept the energy fed back from the motor during the remaining time of the current reduction. 4. Fault indication F030 is triggered in the SIMOREG DC MASTER. 5. The SIMOREG CCP recharges the commutation capacitors again in reverse direction so that a new extinguishing process is possible.
Each time the line voltage is switched on (e.g. by means of a line contactor), the SIMOREG CCP needs approx. 3 s until it is ready for use again because the commutation capacitors first have to be charged.
After one extinguishing process, the SIMOREG CCP requires some time before it becomes operational again. This duration depends on the actions during the extinguishing process and immediately afterwards.
Firstly, the surge absorbing capacitors in the SIMOREG CCP must be recharged to the required value (approximately 10 s). Secondly, the chopper resistors that during the armature current reduction convert the energy to heat need a cooling time which is calculated by a software algorithm. Depending on the energy to be extinguished, this time can be as long as approximately 20 minutes.
The SIMOREG DC MASTER contains setting and display parameters for the commissioning, operation, monitoring and diagnostics of the SIMOREG CCP. The status of the SIMOREG CCP is signaled via connectors and triggering of the SIMOREG CCP or faulty statuses are signaled via fault and alarm messages.
The necessary data transfer between the SIMOREG DC MASTER and SIMOREG CCP takes place via the serial interface.