how vector surge relay works ?

Answers were Sorted based on User's Feedback

how vector surge relay works ?..

Answer / birendra singh mehra

Vector shift and ROCOF are basically the same. It is a
function that will disconnect the generator from the grid
in case the grid disappears (black out of the grid/ loss of
mains/ mains failure).

Vector shift and ROCOF are basically the same. It is a
function that will disconnect the generator from the grid
in case the grid disappears (black out of the grid/ loss of
mains/ mains failure).
This function is necessary because in case the grid
returns, it is likely that the generator will not be
running synchronously with it anymore. Thus this would
cause a short circuit.
This type of protection is called either Rate of change of
Frequency (ROCOF or df/dt) or vector shift/ vector surge.
The only difference is the way the set point is expressed.
ROCOF type is used in UK while the rest of Europe usually
uses vector shift.
This relay will trip the generator in case the frequency
changes more than a certain set point within a certain
amount of time. Thus the adjustment is done in Hz per
second [Hz/s] (if the frequency changes more that XHz per
second the relay will trip). The frequency change appears
because the load situation on the generator will change
suddenly in case the grid is lost. This load change causes
a change in the engine speed which is equal to a frequency
Function principle of the ROCOF Relay:
Practically the ROCOF relay will detect zero crossings of
the generator voltage. It measures the time between the
zero crossings and calculates a new frequency after each
zero crossing. In case the frequency changes too much since
the last zero crossing, the relay will trip.
Vector Shift Relay
This relay will trip the breaker in case it detects a phase
shift in the generator voltage. For example if a zero
crossing occurs some degrees earlier or later than
expected. Thus the adjustment is done in degrees.
The vector shift is again depending on the change of the
generator frequency. In case the grid is lost, this will
result in a sudden change of the generator frequency. A
change in frequency will move the zero crossing of the
generator voltage earlier (in case the generator load has
dropped) or later (in case the generator load has
increased). This shift is expressed in degrees. If this
vector shift is larger than a certain set point the relay
will trip.
Function principle of the Vector Shift Relay:
As you can see from above the Vector Shift relay will also
detect zero crossings of the generator voltage. It compares
the calculated zero crossing from the previous periods with
the latest zero crossing. If the difference is larger than
the set point, the relay trips.
Conclusion 1
As you can see from the function principles of both relays,
they are actually the same. Both relays rely on detections
of zero crossings of the generator voltage. The only
difference is the way how the trip level is expressed.
The utility companies require certain trip levels (just as
marine classification societies). In the UK they request
this in Hz per second, in the rest of Europe in degrees.
This goes so far that one of our customers in Switzerland
who used a T3500 ROCOF relay was forced to buy an
additional Vector Shift Relay in order to meet the utility
companies’ requirements (so they could adjust it in
degrees, not in Hz/s).
Conclusion 2
You can see from above that both relays require a sudden
load change of the generator in order to detect the loss of
the grid (mains failure). In case the generator would be
running parallel with the grid but only supplying as much
power as is used by the local consumers, a loss of grid
would not result in a load change on the generator. The
frequency would not change and thus neither the ROCOF nor
the Vector Shift Relay could detect this.
Therefore the utility companies require a minimum import or
a minimum export in case a generator is to run in parallel
with the grid.
Rate of change of frequency relay (ROCOF)

Is This Answer Correct ?    76 Yes 9 No

how vector surge relay works ?..

Answer / vijay

Vector surge relay compares the previous cycle with the
latest. If there is a considerable import or export ( say
20 % ) of the genrator capacity then a sudden disconnection
of the grid supply will cause either a load throw off in
case of export and load on in case of import. This will
cause the generators either underloaded or overloaded (
over accelerated or deaccelerated ) . This loading and
unloading on the generator will shift the cycle of the
genrator by some degrees. If this difference in cycle is
within the trip setting of the relay the relay will
generate a tripping command.
For example
50 HZ frequecy cycle means 50 Cycle / Second
so 1 cycle will take 20 msec
20 msec = 360 deg ( Angle for 1 full cycle )
1 msec = 18 Deg
If the relay setting is at 9 deg means a time delay of 0.5
msec in crossing of previous cycle happen then the relay
will trip.
If the cycle measurement repetation is of 4 cycle then the
relay will compare the previous 4 cycles.

Is This Answer Correct ?    33 Yes 2 No

how vector surge relay works ?..

Answer / raghupathi

how to calculate the vectorsity of df/dt

Is This Answer Correct ?    9 Yes 2 No

Post New Answer

More Electrical Engineering Interview Questions

Our Slip Ring Induction Motor Frequently tripped By Earth Fault While Starting time and in Normal Operation Time also Kindly Let me Know the Reason. Application Ball Mill - Cement Mill

1 Answers  


0 Answers  

Can we use generator transformer as step down transformer? How?

3 Answers  

How to calculate KW what is the formula for KW.

18 Answers   Toyota, UU,

What is Tachometer used to measure?

0 Answers   Blue Star,

what is different between kvar & micro farad when its comes across the capacitor rating is it possible to convert kvar to mf or mf to kvar

1 Answers   Manipal University,

what will happen if field winding supply of synch generator accidently got disconnected?

4 Answers  

The DC current waveform is - . What about the fire alarm waveform?

1 Answers  

how to 2 phase supply from 3 phase

1 Answers  

What is the difference between online ups and offline ups?

44 Answers   NIT, HCL, UBS, GMR, Electrical Tech, Indus Towers, Gravity India, Pyramid, Techno Electric and Engineering,

Explain advantages of storage batteries

0 Answers  

if our load is 65000 watts howcan we find out all char like cable size. mcccb etc

3 Answers  

  • Civil Engineering Interview Questions Civil Engineering (5070)
  • Mechanical Engineering Interview Questions Mechanical Engineering (4442)
  • Electrical Engineering Interview Questions Electrical Engineering (16579)
  • Electronics Communications Interview Questions Electronics Communications (3915)
  • Chemical Engineering Interview Questions Chemical Engineering (1091)
  • Aeronautical Engineering Interview Questions Aeronautical Engineering (214)
  • Bio Engineering Interview Questions Bio Engineering (96)
  • Metallurgy Interview Questions Metallurgy (361)
  • Industrial Engineering Interview Questions Industrial Engineering (258)
  • Instrumentation Interview Questions Instrumentation (2986)
  • Automobile Engineering Interview Questions Automobile Engineering (332)
  • Mechatronics Engineering Interview Questions Mechatronics Engineering (97)
  • Marine Engineering Interview Questions Marine Engineering (122)
  • Power Plant Engineering Interview Questions Power Plant Engineering (170)
  • Textile Engineering Interview Questions Textile Engineering (575)
  • Production Engineering Interview Questions Production Engineering (0)
  • Satellite Systems Engineering Interview Questions Satellite Systems Engineering (106)
  • Engineering AllOther Interview Questions Engineering AllOther (1376)