To Next Page

To Previous Page

CHAPTER 2: INSTALLATION ELECTRICAL INSTALLATION

845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL 2–21

Phase Sequence and Transformer Polarity

For correct operation of the relay features, follow the instrument transformer polarities,

shown in the Typical Wiring Diagram above. Note the solid square markings that are

shown with all instrument transformer connections. When the connections adhere to the

drawing, the arrow shows the direction of power flow for positive watts and the positive

direction of vars. The phase sequence is user programmable for either ABC or ACB rotation.

The 845 relay has four (4) current inputs in each J slot and K slot. Three of them are used

for connecting to the phase CT phases A, B, and C. The fourth input is a ground input that

can be connected to either a ground CT placed on the neutral from a Wye connected

transformer winding, or to a “donut” type CT measuring the zero sequence current from a

grounded system. The relay CTs are placed in a packet mounted to the chassis of the

845

relay. There are no internal ground connections on the current inputs. Current

transformers with 1 to 12000 A primaries may be used.

CAUTION:

Verify that the relay’s nominal input current of 1 A or 5 A matches the secondary rating

of the connected CTs. Unmatched CTs may result in equipment damage or inadequate

protection.

CAUTION:

IMPORTANT: The phase and ground current inputs correctly measure up to 46 times the

current input’s nominal rating. Time overcurrent curves become horizontal lines for

currents above 20 × PKP.

Ground CT Inputs

Before making ground connections, be aware that the relay automatically calculates the

neutral (residual) current from the sum of the three phase current phasors. The following

figures show three possible ground connections using the ground current input (Terminals

J7 and J8).

The ground input (Terminals J7 and J8) is used in conjunction with a Zero Sequence CT as

source, or in the neutral of wye-connected source CTs. The ground current input can be

used to polarize the neutral. When using the residual connection, set the

GROUND

CT PRIMARY setpoint to a value equal to the PHASE CT PRIMARY setpoint.

Figure 2-23: Ground Inputs

892773A2.cdr

8 Series

J8J7 J8J8 J7

GE 845 User Manual

Questions and Answers: