Siemens 7SR157 Argus, Руководство пользователя

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7SR157 Technical Manual
Chapter 7 - Page 6 of 14 © 2016 Siemens Protection Devices Limited
2.4 Synchronising Bypass Logic
The relay Dead and Live voltage monitors are used along with corresponding internal logic to bypass the
synchronising operation of the relay. Typically, anywhere above 80% to 90% of rating can be classed as a live line
or live bus. The dead voltage monitors should be set to somewhere above the expected level of induced voltages
on the line or bus. It should be noted that a dead line or dead bus can have a considerable potential induced onto
it from a parallel line or via capacitance across open breaker contacts. This potential can be as high as 30% of
rated voltage.
The Sync Bypass logic (found in VOLTAGE SETTING MENU) can be enabled, if required, to provide Dead Line
and Live Bus closing, Live Line and Dead Bus closing, Dead Line and Dead Bus closing, Dead Line or Dead Bus
closing and Dead Line xor Dead Bus closing. A truth table showing the close logic for all of the possible
combinations is shown in Table 1.
Sync Bypass Setting
DL & LB LL & DB DL & DB DL or DB DL xor DB
Line Status Bus Status Allow Close Allow Close Allow Close Allow Close Allow Close
Dead Dead No No Yes Yes No
Dead Live Yes No No Yes Yes
Live Dead No Yes No Yes Yes
Live Live No No No No No
Table 1 - Bypass Close Logic
2.5 Slip Frequency and Phase Angle Relationship
Slip frequency is defined as the difference between two frequencies. Where a slip frequency exists between two
separate systems, during a ‘slip’ cycle the two voltage vectors will be in anti-phase at one point in time. The phase
angle difference will vary between being in phase and anti-phase. The 7SR157 relays can be set to measure slip
frequency in two ways. One way is to measure the two system frequencies directly and calculate the difference.
Another way is to measure the phase difference between the two systems and check that the phase angle change
in a defined time period is less than a predetermined value. If F1 and F2 represent the frequencies of two systems
then it can be shown that for check synchronising operation:
°
× = − = ∆
180 Td
1
2 F 1 F F
θ
where Td = time delay setting ( 25 Check Sync Timer ) and
θ = phase angle setting (
25 Check Sync Angle ).
For system synchronising operation the following formula is used because in this mode the relay will only issue a
close signal if the phase angle is decreasing in value. It will not issue a close if the phase angle is increasing in
value.
°
× = − = ∆
360 Td
1
2 F 1 F F
θ
where Td = time delay setting ( 25 System Sync Timer ) and
θ = phase angle setting (
25 System Sync Angle ).
The 7SR157 relay has both a frequency measuring element and phase detector and so can be set up to measure
slip either directly or by the phase detector plus timer method. Use of either method is perfectly valid, as is use of
both at the same time.
Note : if using both the slip frequency detector and the phase angle plus slip timer for a particular scheme then
care has to be taken in setting selection. It is possible to set the relay up with an incorrect slip timer setting which
will prevent the relay from issuing a valid close signal e.g. a system with a high rate of slip which is within the
allowable slip frequency limit, could be set up with too long a slip timer setting. This would mean that the incoming
vector could pass through the valid close window too quickly and not allow the slip timer to time out and give a
valid output.