HOW TO SYNCHRONISE A GENERATOR?

I can tell you how it used to be done, things are more automated now but its good to know the basics.

The basic philosophy is that the AC waveform of the generator must superimpose on top of the system waveform, attempting to connect while the generator waveform is at a peak and system is at zero or maximum negative value will result in a big bang.

The traditional method involved a clock meter with a single rotating needle and the stationary mark at 12.00, the segments either side of 12.00 were labelled Slow and Fast. While watching this meter the operator would have control of the generator speed and the closing switch for the generator circuit breaker.

Th speed and position of the clock needle represented the generator waveform with the 12.00 mark representing the zero part of the system waveform.

By increasing or decreasing the generator shaft speed the needle can to be made to hover over or close to the 12.00 position, when the circuit breaker can be closed. Once connected the generator shaft speed is controlled by the governor which for a 2 pole 50 Hz machine would be 3000RPM

Failure to maintain the shaft speed by overloading say causes a change in the output frequency which trips the generator circuit breaker.

This was the standard procedure for power stations in the UK, before more automated systems took over. It can also be achieved by using a series of lamps indicator instead of the clock meter.

To explain it very simplistically:

First, there must be continuity of the poles of each generator.

A light bulb is connected between each matching phase, hence three phases, three light bulbs.

If the phases (think in terms of the sine waves themselves) are not synchronized, there is a potential voltage between them and the light bulbs light up. The more they are out of phase, the brighter the bulbs. All bulbs will brighten and darken together because the phases are rotating together. They will be their brightest when 100% out of phase.

When the lights are completely dark, the generators are in sync.

The above mentioned synchronizing meter is used to determine whether the 'on-coming' gen set is going faster or slower. The rate of intermittent flashing and on-off of the lights only tells you that the generators are not in sync, not whether one is faster than the other. Before these meters, tachometers were used.

In older equipment, without all of the new control mechanisms, the oncoming generator should always be rotating just slightly faster (the lights dark every second or two) than the loaded gen set. This gives it some capacity to take a small portion of the load upon parallel. The manual switch gear is engaged just before the lights darken so you have time for the contacts to engage.

If it is going slower or exactly the same same speed as the loaded generator, there is the possibility of motorization, a very, very bad thing. When this happens, the generator on line actually motorizes the other causing it to come to an extremely abrupt halt and rapid acceleration of what is left in the other direction. If you're still alive, you will lose your job for sure. This is why the very important reverse current relay/switching gear was developed for all applications.

Do not attempt to parallel generators that do not have a mechanism for load control!

Do not attempt to parallel generators that are not of equal electrical capacity and prime movers, and or do not have the same electrical and governor regulation/characteristics!

There are some point we have to know in order to syncronize 2 generators:

1). Frequency must be equal

2) Order of phases must be the same

3). Voltage must be equal

But,How do we match respective phases like R to r , Y to y ,B to b .Methods adopted to find out respective phases is very important.It has to be elaborated further.Recently, We synchronized TG set with DG set.Before synchronizing ,we checked, voltage,frquency,phases,even polarity checking also.We used woodward make synchronizer & in the background syunchronoscope,also dark lamp method .If all the lamps are geting bright and dark simultaneously then phases are same.If phases are interchanged then all three lamps will get bright and dark one after the other.

First we identified the running R,Y, B phases as reference.Then we matched the incoming R,Y,B phases in the 11 KV feeder through 11kv/110V transformer at the time all three lights were getting Bright and Dark together.

Then,We changed purposefully R to y,Y to r ,B to b.This time lamps were getting brighter one after another.

Again,we changed the connection R to y, Y to b, B to r. This time all three lamps are getting brighter and darker together.

Result;Phase sequence is same.

Can anybody suggest to findout the exact method to find exactly R,Y,B phases of incoming supply correctly.

P.Mathurboothem

My reply:
To:
koshy.dennis
HOW-TO-SYNCHRONISE-A-GENERATOR
??? to which ???
1. Another generator or
2. The Power Mains
3. Sychronising a Generator to the Mains which failed & load was shifted on generator
automatically as a redundant-source or manually put on generator after Mains failure.



Guest post #1 has described it well in old systems where it was done manually.


Auto Sync
---------
In case 1. although you have both the generators in control, yet Gen under load is taken as ref
and other is sycronized to it.

in case 2. & 3. Mains is the REF & Generator is syncronized to it.

A Sync-board is normally used in system which keeps the CB of generator locked till the frequency & Phase-angle are in sync and output voltage are within some limits. All the conditios are indicated on control-panel. As soon as all the parameters are OK clear signal is indicated. If the system is put on auto-shift [connect] it is done automatically or by the operator if on "Manual-Shift".


Reply to:
Guest #1


Really well defined Manual-Shifting of load from Generator to Mains Supply.

thanks for ur comment

i want to know how the bright light method is?(old one)

The first thing to do is turn off Caps Lock. That would be a good start.

It pays also to be polite. Take the risk.