Schweitzer Engineering Laboratories SEL-311C, Инструкция по эксплуатации

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Date Code 20060320
Instruction Manual SEL-311C Relay
Section 3
Distance, Out-of-Step, Overcurrent,
Voltage, Synchronism Check, and
Frequency Elements
Distance Elements
Mho Phase Distance
Elements
The SEL-311C Relay has four independent zones of mho phase distance
protection. All zones are independently set. Zones 1 and 2 are fixed to operate
in the forward direction only. Zones 3 and 4 can be set to operate in either the
forward or reverse direction. The phase distance elements use positive-
sequence voltage polarization for security and to create an expanded mho
characteristic. The phase distance elements operate on phase-to-phase, phase-
to-phase-to-ground, and three-phase faults.
Compensator distance elements are included for distance relaying through
wye-delta transformer banks and for users who desire a different operating
principle for backup relaying. Compensator distance phase-elements
implemented in the SEL-311C detect phase-to-phase, phase-to-phase-to-
ground and three-phase faults.
Operating Principles of Phase Distance Elements
A digital relay mho element tests the angle between a line drop-compensated
voltage and a polarizing (reference) voltage using the following concepts:
Sampled currents and voltages are represented in the relay as vectors by using
the most recent sample as the real vector component and the sample taken one
quarter cycle earlier as the imaginary vector component. See
Figure 12.4 and
Figure 12.5 in Section 12: Standard Event Reports and SER for a description
of this process.
➤
If vector V
1
= |V
1
|
∠ θ
1
and vector V
2
= |V
2
|
∠ θ
2
, then
V
1
• (V
2
conjugate) = V
1
• V
2
* = [ |V
1
| • |V
2
| ]
∠
(
θ
1
–
θ
2
)
The angle of the vector quantity V
1
• V
2
* is the test angle of the
mho element.
➤
Test for V
1
• V
2
* balance point at
θ
1
–
θ
2
= 0 degrees by
calculating sin (
θ
1
–
θ
2
). In a digital relay, this is done by
examining the sign (+ or –) of the imaginary component of V
1
•
V
2
*, written Im (V
1
• V
2
*).
➤
Test for V
1
• V
2
* balance point at
θ
1
–
θ
2
= 90 degrees by
calculating cos (
θ
1
–
θ
2
). In a digital relay, this is done by
examining the sign (+ or –) of the real component of V
1
• V
2
*,
written Re (V
1
• V
2
*).