Plan the Generator Current Transformer (CT) Location

Related Products:

EMMK-101, EMMK-102, EMMK-103, EMMC-104, EMMC-105, EMMC-106

Related Documents:





generator CT, NGT, frame ground, RTD leads, RTD termination box


Guidance for planning the location of the Generator CT components: Neutral Ground Transformer (NGT), Frame Ground, RTD Leads, and RTD Termination Box.

Plan the Generator Current Transformer (CT) Location

This article provides guidance for planning the location of the Generator CT components:

  • Neutral Ground Transformer (NGT)

  • Frame Ground

  • RTD Leads and RTD Termination Box

Neutral Ground Transformer (NGT)

If the installation has a stand alone NGT cabinet and the lead coming into the NGT cabinet is in a conduit of a size that the EMMC-106 (127 mm) CT can fit around:

  1. Open the EMMC-106.

  2. Place the CT around the outside of the NGT lead conduit.

  3. Latch the CT closed.

This preferred location gives the best EMI signal strength.

If the installation does not have a stand alone NGT cabinet or the lead coming into the cabinet is too large for the EMMC-106 CT, then place the CT around the cable going into the high side of the neutral ground transformer. This option is not preferred because:

  • It requires a plant outage to perform

  • The neutral ground lead must be insulated to the full generator output voltage

  • CT must be restrained from moving or touching the cable


If the CT comes into contact with the cable, it may cause damage to the cable insulation and cause the NGT to be bypassed in a phase to ground fault condition. This condition could cause very high currents to be generated during the fault condition and cause major equipment damage.

Frame Ground

For locations where the NGT is inaccessible, you can use a generator frame ground for the CT location.

Portable monitoring with an interference analyzer should be performed during unit on line conditions to determine which frame ground location has the best signal strength.


The best signal is not always the one with the with the highest value but the one with the most internal noise values.

After the location has been determined, the vendor will most likely use the EMMC-104 (32 mm) CT. Some vendors use only the EMMC-106 CT for all monitoring purposes, but the EMMC-104 CT has similar response characteristics and is more cost effective.

For many Combustion Turbine Generators, the Exciter end frame ground is the lead of choice. Take care that the CT around the frame ground is coming directly from the frame casing and is not a combination of multiple ground leads. Having multiple ground leads introduces external noise and hampers the analysis process.

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