Without further information, suggest odds are better than average that one will find the weak link in a hurry when tied together, in rather dramatic and perhaps career-ending fashion.
Synchronization requires that voltage, frequency, rotation, and phase be within tolerances to gain the permissive to tie on.
'without synchronisation' - did you mean the switchboard is not connected to grid??
If true, there shouldn't be any issue as long as the droop settings of both the generators are same, they will share the load equitably.
Some times, the governors and AVRs are interconnected so that one of them can be master giving signals to governor / AVR of the other unit. This way, the sharing of load and VARs will be identical.
I am not considering the case of connecting the generator to already live switchboard without synchronisation.
If you close a tie between two generators 180 degrees out of phase, the voltage driving the circulating current between the two generators will be twice rating, and the resulting current can be as much as double predicted bolted fault current.
If there is a transformer in the circuit - for example closing in out of phase with the utility, expect to see mechanically ruptured transformer wingdings. Your reverse power protection probably will not react fast enough, and even fuses might not be fast enough to prevent damage.
A bit of poking at google turned up a paper on the subject. The paper shows a method of figuring out which components are at risk.
Consequences of Out-of-Phase Reclosing on Feeders With Distributed Generators
Dale Williston, Williston & Associates Inc.
Dale Finney, Schweitzer Engineering Laboratories, Inc.
Start with some textbooks; I have quite a number of these that explain the technology quite well. This will also be of benefit to you in framing less ambiguous questions.
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
Actually the one in Russia was water hammer and flood damage.
Step one was when they closed the control gates too fast and water hammer ruptured the penstock.
Step two was when the rapidly rising water in the generator hall contacted the bottom of the horizontal rotor.
The spinning support girders of the horizontal rotor acted like the vanes of an under designed centrifugal pump and the mechanical forces ripped the rotor loose.
Several workers in the lower levels were drowned.
The initial damage was hydraulic and mechanical.
Bill
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"Why not the best?"
Jimmy Carter
If the generators are out of phase, out of step or out of synchronization, the result depends on how far out.
If the generators are free running the relative positions are random and may be described by a random number of degrees between 0 and 180 degrees.
Based on diesel generators in the range of 350 kW to 600 kW;
Up to about 5 degrees error the sets will pull into sync benignly.
As the angle becomes greater the electrical transients become greater and the mechanical forces increase.
One set has a positive torque transient and the other set has a negative torque transient as they try to match angular positions.
With our sets, until I discovered that there was a wiring error introducing a 30 degree error into the synchroscope, the breaker would trip at around 25 to 30 degrees error.
Once or twice a year a key in a coupling would shear.
I don't know if from a greater angular error or from cumulative effects.
The effect depends on the protection, bot current setting and any time delays.
The keyway keys may have acted as a mechanical "Fuse".
This is one example but there is not a representative example.
The electrical effects will depend on first the ability of the protection system to clear instantly and on the mechanical construction and mechanical weak points.
If the protection fails to clear then the physical arrangement and bracing of the windings becomes relevant.
The worst torque transients are at 90 degrees error.
The highest electrical fault currents will be at 180 degrees error.
Large station step-up transformers have been destroyed by an out-of-sync closure.
In the worst instances, when the noise subsides, the smoke clears and the metal cools, the investigations begin.
Further effects may be letters of reprimand, disciplinary actions, terminations and ruined careers.
Lawsuits are a possibility.
Bill
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"Why not the best?"
Jimmy Carter
