Differential Cts Setting Guidelines - GE P4A Technical Manual

Chapter 13 - Supervision
4.6.2

DIFFERENTIAL CTS SETTING GUIDELINES

The Phase Is1 CTS setting must be set above the phase current of the maximum load transfer expected, normally
at 1.2 In. This setting defines the minimum pick-up level of the current differential protection once the current
transformer supervision CTS is detected.
The CTS i1> setting, once exceeded, indicates that the circuit is loaded. A default setting of 0.1 In is considered
suitable for most applications, but could be lowered in case of oversized CTs.
The CTS i2/i1> setting should be in excess of the worst unbalanced load expected in the circuit under normal
operation. It is recommended to read out the values of i2 and i1 in the MEASUREMENTS 1 column and set the ratio
above 5% of the actual ratio.
The CTS i2/i1>> setting should be kept at the default setting (40% In). If the ratio i2/i1 exceeds the value of this
setting at only one end, the CT failure is declared.
Note:
The minimum generated i2/i1 ratio will be 50% (case of one CT secondary phase lead being lost), and therefore a setting of
40% is considered appropriate to guarantee sufficient operating speed.
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