Current Transformer Inputs; Ground Current Transformer Input; Contact Outputs; Figure 2.10 Ground Ct Placement - Siemens SIMPRO-100 Instruction Manual

2
Installation
2.4.3 Current Transformer
Inputs
The SIMPRO-100 Relay is equipped with four
current transformer inputs: IA, IB, IC, and IN.
Each input can accept either 1 A nominal or 5 A
nominal CT secondary inputs.
The relay sequence current and power
measurements are sensitive to the polarity of
current applied to the relay. Make sure that the
current connections observe the polarity
markings shown in Figure 2.6 and Figure 2.7,
page 30. Connect the CT nonpolarity lead to the
COM CT terminal. Connect the CT polarity lead
to the 5 A or 1 A input, depending on the
secondary rating of the CT.
Select the phase CT ratios so that the motor full
load current is greater than 50% of the CT
primary rating.
Example: Phase CT Ratio Selection
A 200 HP, 575 V, three-phase motor draws
192 A at full load. Use one of the following
CT ratios:
• 200:5 (200 x 0.5 = 100)
• 250:5 (250 x 0.5 = 125)
• 300:5 (300 x 0.5 = 150)
• IFLA = 192 > 100; 125; 150
2.4.4 Ground Current
Transformer Input
The relay IN input can be connected in either of
two ways, as shown in Figure 2.6 and Figure 2.7,
page 30. The preferred method is the ground CT
method in Figure 2.6, page 30. Connecting the IN
input residually, as in Figure 2.7, page 30,
requires you to select a relatively high
overcurrent element pickup setting to avoid
tripping due to false residual current caused by
CT saturation during high starting current. The IN
connection shown in Figure 2.6, page 30 is
preferred and provides for a lower ratio
flux-balance CT that avoids saturation and
provides greater ground fault sensitivity.
32
When you use a ground CT, its placement is
critical and depends on the type of cable used to
connect the motor to the source. As Figure 2.10
shows, using unshielded cable requires that the
CT be placed between the neutral connection to
ground and the motor, with the neutral lead
included in the CT window. With shielded cable,
the shield connection to ground must pass
through the CT window.

Figure 2.10 Ground CT Placement

2.4.5

Contact Outputs

The SIMPRO-100 Relay is equipped with five
contact outputs. Each one provides a normally
opened and a normally closed contact. The
contacts are rated to switch 8 A resistive at 250
Vac. For dc operation, the contacts are rated for
tripping duty, according to IEEE standards.
The contact positions indicated in Figure 2.11,
page 33 and on the relay chassis are the
positions the contacts are in when the relay is
deenergized. The relay self-test ALARM contact
always operates in a fail-safe mode; you can use
relay settings to program the remaining outputs
for fail-safe operation. When you set an output to
SIMPRO-100
PRIM-2400C