Schweitzer Engineering SEL-351P, Быстрый старт

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Date Code 990430 Overcurrent, Voltage, Synchronism Check, and Frequency Elements 3-39
SEL-351P Manual Técnico
V
S
Synchronism check voltage, from SEL-351P rear-panel voltage input VS
For example, if V
P
is designated as phase input voltage V
B
(setting SYNCP = VB), then
rear-panel voltage input VS is connected to B-phase on the other side of the circuit breaker. The
voltage across VB is synchronism checked with the voltage across VS (see Figure 2.1).
System Frequencies Determined from Voltages V
A
and V
S
To determine slip frequency, the system frequencies on both sides of the circuit breaker need to
be determined. Voltage V
S
determines the frequency on one side. Voltage V
A
determines the
frequency on the other side. Thus, voltage input VA has to be connected, even if another voltage
(e.g., voltage V
B
) is to be synchronized with voltage V
S
.
In most applications, all three voltage inputs VA, VB, and VC are connected to the three-phase
power system and no additional connection concerns are needed for voltage connection VA-N.
The presumption is that the frequency determined for A-phase is also valid for B- and C-phase in
a three-phase power system.
However, for example, if voltage V
B
is to be synchronized with voltage V
S
and plans were to
connect only voltage inputs VB and VS then voltage input VB will also have to be connected for
frequency determination. If desired, voltage input VA can be connected in parallel with voltage
input VB. In such a nonstandard parallel connection, remember that voltage input VA is
monitoring Phase B. This understanding helps prevent confusion when observing metering and
event report information or voltage element operation.
Synchronism Check Elements Operation
Refer to Figure SECTION 3: .24 and Figure SECTION 3: .25.
Voltage Window
Refer to Figure SECTION 3: .24.
Single-phase voltage inputs V
P
and V
S
are compared to a voltage window, to verify that the
voltages are “healthy” and lie within settable voltage limits 25VLO and 25VHI. If both voltages
are within the voltage window, the following Relay Word bits assert:
59VP indicates that voltage V
P
is within voltage window setting limits 25VLO and 25VHI
59VS indicates that voltage V
S
is within voltage window setting limits 25VLO and 25VHI
As discussed previously, voltage V
A
determines the frequency on the voltage V
P
side of the
circuit breaker. Voltage V
A
is also run through voltage limits 25VLO and 25VHI to ensure
“healthy voltage” for frequency determination, with corresponding Relay Word bit output 59VA.
Other Uses for Voltage Window Elements
If voltage limits 25VLO and 25VHI are applicable to other control schemes, Relay Word bits
59VP, 59VS, and 59VA can be used in other logic at the same time they are used in the
synchronism check logic.