Ground Fault Current Transformers
Function:
Ground Fault Current Transformers (CTs) are a window type ground fault sensor. We use these current transformers to sense zero-sequence ground-fault currents. We also call them core-balanced current transformers (CBCTs).
These units detect the presence of zero sequence currents during short circuit fault conditions. For example, the occurrence of a single line to ground fault that causes unbalanced currents in three-phase systems.
Requirements:
Ground Fault Current Transformers require technicians to route all three phase conductors and the neutral (in a four-wire system) through the window of a single current transformer. Under normal conditions the current transformer will not see any current. This is because the sum of a balanced three phase system is zero, thus the name “Zero Sequence”. In as much as all three phases and neutral (if there is one) must pass through the same window. This requires a current transformer with a large window to accommodate all of the conductors.
During abnormal operations, the occurrence of a single phase to ground fault causes current imbalances in the three phases. If the vector sum of the phase currents is not zero, the core of the zero-sequence current transformer generates magnetic flux, and the ground fault relay detects the resulting current.
We rate all units listed here at 600 V, and you can operate them at higher voltages with fully insulated cables. When you deploy a low-voltage window-type CT in a higher-voltage system, ensure the operating conditions are met and take the necessary precautions.
What is a Current Transformer?
A Current Transformer (CT) reduces or multiplies an alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary.
Current Transformers, along with voltage or potential transformers, are instrument transformers. Instrument transformers scale the large values of current to small, standardized values. These are easy to handle for measuring instruments and protective relays. The Instrument transformers isolate measurement or protection circuits from the high voltage of the primary system. These units provide a secondary current that is accurately proportional to the primary current. They present a negligible load to the primary circuit.
Power system engineers rely on these units as current-sensing devices at generating stations, electrical substations, and in industrial and commercial power distribution.
Advantages:
Advantages of Current Transformers are that the units can measure high current easily, high electrical isolation, simple construction, and easy maintenance and installation.
Features:
- Different ratios available
- Variety of Window Openings
Applications:
Approvals:
- CSA
- UL
Ground Fault CT (same as Zero Sequence CT)
- CSA
- UL