The object of this type of testing is to ensure the correct operation of protection, which in a properly designed installation will limit damage to the system in the event of a fault. All faults detected are recorded and reported for remedial action as required. For example if the unit under test is tripping quicker than its designated curve time this does not necessarily mean that it has to be replaced, in fact it could be reported and left in circuit so long as it does not cause regular nuisance tripping. Should remedial work be required the ERIKS site engineers are trained in all aspects of switchgear /protection maintenance.
The following tests should be carried out to ensure safe efficient operation.
- Contact resistance and I.R. readings
- Injection Testing
- Function Test
This test should be carried out on the Circuit Breaker ensuring all connections, mountings etc are secure. Attention should be paid to arc suppressors, circuit breaker mechanism and contacts. Long Time Delay (LTD), Short Time Trip and instantaneous settings should be checked against as fitted drawings, should they not be available the ERIKS Engineers are able to produce a single line drawing depicting the relevant settings and fault currents.
Long Time Delay (LTD)
can be any of the following:
- 1) Thermal inverse o/c
- 2) Magnetic with time delay (definite time)
- 3) Electronic (definite time or inverse o/c
Where applicable the above would be checked against manufacturers curves. Normal ERIKS practice would be to inject at three (3) times the set current. However the site engineers are able to adapt the duration or test to suit the individual case ensuring the value of minimum trip and accuracy of time delay.
Short Time Trip
These units are either magnetically or electronically operated. It is essential that this unit is not tripped by either the LTD or Instantaneous trip.
In this case the current is raised until the unit trips instantaneously however care must be taken to ensure that neither the Long Time Delay nor Short Time Trip operate. Care must be taken to ensure that the minimum tripping current is recorded. On completion of all tests the settings are returned to their correct values.
Injection Testing Normally
two methods or a combination of both protects circuit breakers.
- 1) Internal Tripping Units
- 2) External Tripping Units
Internal Tripping Units
These breakers require Primary Injection; non-withdrawable units are disconnected from the board and tested remotely.
External Trip Units
Operate through an undervoltage or shunt trip coil. These devices are C/T operated and can be tested by Secondary Injection.
The following tests should be carried out
- Overcurrent Trip Time (cold)
- Overcurrent trip Time (hot)
- Minimum Trip Time
Prior to testing the motor current should be checked to ensure correct unit is installed.
Overcurrent Trip Time
Three phases are linked and current injected at 3 times FLC setting.
Minimum Trip Time
These are checked against manufacturers settings.
All of the above tests come with detailed ERIKS test reports and curves.