GE350 Feeder Protection System

transformer polarities, shown in the Typical Wiring Diagram. Note the solid square 

markings shown with all instrument transformer connections. When the connections 

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

the positive direction of lagging vars.The phase sequence is user programmable for either 

ABC or ACB rotation.

Current inputs

The 350 relay has four (4) channels for AC current inputs, each with an isolating 

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

transformers with 1 to 6000 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 will correctly measure up to 20 

times the current input’s nominal rating. Time overcurrent curves become horizontal 

lines for currents above the 20 × CT rating. This becomes apparent if the pickup level is 

set above the nominal CT rating.

CAUTION: Before working on CTs, they MUST be short circuited.

Ground and sensitive ground CT inputs

One dedicated ground input is referred to throughout this manual as the Ground Current

or Sensitive Ground Current input. Before making ground connections, consider 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 (or 

three possible sensitive ground connections).

The ground input (Terminals D8 and E8) 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 directional element. When using the residual connection set 

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

In cases where the relay is equipped with sensitive ground CT (terminals D8 and E8) the 

sensitive ground current input is intended for use either with a CT in a source neutral of a 

high-impedance grounded system, or on ungrounded systems. On ungrounded systems it 

is connected residually with the phase current inputs. In this case, the SENSTV GND CT 

PRIMARY setpoint should be programmed to a value equal to the PHASE CT PRIMARY 

setpoint. The sensitive ground current input can be connected to a Zero Sequence CT for 

increased sensitivity and accuracy when physically possible in the system.

NOTE

NOTE: The Sensitive Ground input must only be used on systems where the maximum ground 

current does not exceed current input specifications

Zero sequence CT installation

The various CT connections and the exact placement of a Zero Sequence CT, for ground 

fault current detection, are shown in the figure below. Twisted pair cabling on the Zero 

Sequence CT is recommended.

Figure 2-35: Zero sequence core balance (CT) installation

Voltage inputs

The 350 relay has four channels for AC voltage inputs, each with an isolating transformer. 

Voltage transformers up to a maximum 5000:1 ratio may be used. The nominal secondary 

voltage must be in the 50 to 240 V range.The three phase inputs are designated as the “bus 

voltage”. The Bus VT connections most commonly used, wye and delta (or open delta), are 

shown in the typical wiring diagram.

NOTE

NOTE: If Delta VTs are used, the zero sequence voltage (V0) and neutral/sensitive ground 

polarizing voltage (–V0) will be zero. Also, with the Delta VT connection, the phase-neutral 

voltage cannot be measured and will not be displayed.

NOTE

NOTE: The 350 relay can be applied to both metering and protection feeders with up to 550 kV 

phase-to-phase voltage. Please ensure that the selected VT ratio and VT secondary do not 

result in a primary voltage exceeding 550 kV.

The single phase input is designated as the “Aux VT Input”. The Aux VT input channel can be 

connected for either phase-neutral voltage Van, Vbn, Vcn, or for phase-phase voltage Vab, 

Vbc, Vca as shown below.

Control power

CAUTION: Control power supplied to the relay must match the installed power supply range. If the 

applied voltage does not match, damage to the unit may occur. All grounds MUST be 

connected for safe, normal operation regardless of control power supply type.

The label found on the relay specifies its order code or model number. The installed power 

supply’s operating range will be one of the following:

LO: 24 to 48 V DC (Range: 20 to 60 V DC)

HI: 125 to 250 V DC/120 to 240 V AC (Range: 84 to 250 V DC/60 to 300 V AC (50 and 60 

Hz))

CAUTION: The relay should be connected directly to the ground bus, using the shortest practical 

path. A tinned copper, braided, shielding and bonding cable should be used. As a 

minimum, 96 strands of number 34 AWG should be used. Belden catalog number 8660 

is suitable.

CAUTION: Isolate power prior to servicing.

An external switch, circuit breaker, or other protective device must be connected near to