The correct operation of the protection relay can be confirmed to a certain extent by means of secondary injection testing, as it is always more or less simulated situation.
During primary earth fault testing, a controlled actual earth fault is performed and thus the behavior of the entire network in the event of a fault can be observed, including relays from healthy feeders. A properly executed primary test reveals errors that may have been unnoticed during secondary injection testing.
Execution of Primary Earth Fault Test
The primary earth fault test can be done with the light setting, where the fault is made by closing the circuit breaker of the feeder while the fault is connected. In most cases, every significant point about correct operation of earth fault compensation and protection relays can be confirmed by using this method.
However, the best results and the most realistic faults are obtained by using an earth fault testing with a fault cart designed and built for this purpose. This allows the fault to be connected directly at the fault location, and it can be performed while the network is in normal use.
Versatile Coupling Options
The fault cart can be connected to live overhead lines and the earth fault testing can be done without interruptions in distribution. To a disconnected feeder, the cart can be coupled to any air-insulated sections of overhead lines or secondary substations. By choosing different cables, connection to SF6 switchgear is also possible.
The duration of the fault can be set shorter than operation delay of the feeder’s protection, if actual trip is to be avoided. Earth fault cart is equipped with accurate measuring transformers and a disturbance record is created for each fault. Disturbance recordings can be analyzed immediately on site..
The equipment of the fault cart is top-notch
- 3-phase connection to live overhead lines, cable length 20m
- Separate cables with 630 A plug connectors
- Comprehensive variety of resistors for earth fault tests (0-100 kΩ)
- Spark gap for restriking faults
- 24 kV switchgear, nominal current 630 A
- Ring main feeder
- Motor operating three-position switch-connector and an earthing switch
- Voltage indicators
- Billing metering panel
- Phase voltage transformers 20 VA / Cl. 0,2
- Open delta winding 100/3 V, 25 VA / 3P
- Current transformers 400/5/5, 5 VA Cl. 0,2FS5, 5VA Cl. 5P10
- Circuit breaker feeder
- Manually operating three-postition switch-connector and an earthing switch
- Vacuum circuit breaker 630A
- Rated short-circuit breaking current Isc: 20.0 kA
- Protection relay with disturbance recorder
- Adjustable fault duration
- Connectors for exernal measuring devices
- DC-supply (110VDC ja 12VDC)
- 230 VAC generator
- Earthing electrode rods
