Hydro Generator Paralleling

[Viceng]

Hi, I was wondering if anyone here could highlight possible issues faced with paralleling two HRG Hydro generators (same manufacturer, same size, same speed) to a common 5kV bus, and subsequently out to the utility through a common transfomer.

Assuming, both generators have same type of voltage regulators with the same type of droop compensation (hopefully avoiding circulating currents) what other issues may there be to look out for?

Thanks!

 

[dpc]

You will need proper synchronizing equipment and governor controls to make sure synchronize one generator to the other or to the power grid. The utility will also require a substantial amount of protective relaying. Voltage matching will be the easiest part, really.

Check Basler and Woodward websites for technical data on parallel operation of generators.

 

[Viceng]

Thanks DPC,
Basler definitely has some good documentation.

 

[waross]

Once you are online you will set the power output (KW) with the main water control valve. The voltage regulator will control the reactive current.
You can probably get online and export to a utility with almost any governor settings, but if the sets are going to be islanded at any time, the governor characteristics and settings should be the same.
respectfully

 

[mottt]

if you couple to the utility you only need a AVR regulator and a PFC regulator ( maybe the same device in example Basler...ABB), this will control the reactive of the generators, that must be inside the capacitive curves... or to work in a fixed power factor. In the side of the kw you need a control for the turbine... maybe Woodward, Voith...Vatech..or other manufacturers....
In the couple to the grid.. you could use a regulator with a voltage matching.. or to raise or reduce voltage with your syncro device working on the AVR... the same with the frequency, you will control the speed regulator with the syncro device... there´s a lot of manufacturer... and you could adjust the window of syncronism... depending on the generator and the utility, you could use a more or less restrictive window...
About protections, i think you will need... in all the sizes of machine... Overvoltage, minimum voltage, overcurrent protections, to earth, overload, between phases with differents curves for trip... and it´s needed to know the way it´s grounded cause depending on this you will use one adjustment or other....reverse power, excesive capacitive (seen from the machine side) current... if you use a Basler 200 you got inside regulator... differencial protection on the generator side and transformer...
I like a lot the multiline (GE) or Sepam ...
If your work on a separated grid, the thing is more easy,
you´ll work normally on droop or cross compensation, and the idea is to make the two machines take the same amount of reactive load, and in the governor side, for the speed, is the same, with the same load.. the governor have to be with the same droop...you could adjust it a little high from the 60 or 50 hz...
i hope this will help

 

[mottt]

maybe i have forget some protection... i´m just thinking fast on them

 

[Viceng]

I appreciate the input.

Waross, sounds like once we are tied to a grid (especially since there are small units - 5MW each), there really aren't many concerns (different from a single generator facility) after ensuring the regurlators are set similarly.

motoxplosion, as you mention there are some strict protection requirements both posed by the utility and ourselves on these units. I am confident we have met all requirements in this regard.

 

[waross]

The grid will set the voltage and the frequency.
Voltage regulator settings will set VAR production.
Governor speed setting and governor droop will control KW production. The droop setting is not very important, BUT, if you have two machines that are paralleled and may be islanded with a significant load, such as an industrial plant that produces enough power to supply in plant needs and also export power, the droop settings should match as close as possible.
When two machines with unequal droop settings are paralleled AND islanded, they may be set to share the load at ONE power level. Either an increase or decrease of the load may cause unequal load sharing to the point that one machine is overloaded.
Good practice dictates that the governors be set as close as possible, despite what will work and what you can get away with.

 

[ScottyUK]

The grid will set the voltage and the frequency.
Voltage regulator settings will set VAR production.

True if the generator is small relative to the grid at the point of connection. A pair of 5MW generators will likely be able to exert significant influence on the voltage of a distribution system unless they are connected close to a major distribution node where the system is 'stiff' and able to absorb VArs without significant voltage variation. It is not unusual to run the AVR in power factor control at a near-unity PF.


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Sometimes I wake up Grumpy.
Other times I just let her sleep!

 

[waross]

Yes ScottyUK. Thanks for correcting me. Now that you remind me, I remember seeing a situation and discussing it with one of the utility engineers.
An old worn out diesel generating plant that was mothballed when the transmission lines from a new, remote hydro generating station arrived in town.
Twenty or more years later the old diesels were started up and put online at low throttle settings (low KW output) and high excitation to supply VARs to both reduce the line losses and to boost the terminal voltage of the transmission line.
Respectfully

 

[Viceng]

ScottyUK, Good point. I neglected to mention that the we are tying into a 69kV system...quite stiff near a very large generating facility.

Our intention (if the Utility allows) is to run in PF mode at or near unity, but often times we are requested to assist with voltage support.

From what I can tell from these responses there are not many issues to be concerned with when parelling two units. I was interested to see whether there would be comments such as: utilize a single HRG between both units not one HRG connection for each, or make sure to use cross current compensation not droop etc.

Thanks,

 

[ScottyUK]

Does each unit have its own GSU transformer or do the generators parallel to a common LV bar with a shared transformer? Is the transformer LV delta or LV star? What else shares that bar with the generator(s) and how is it grounded? In a perfect world you would have a single dedicated GSU tranformer with an LV delta winding and HRG on the generator. I suspect you don't have this ideal situation but is is difficult to comment on the grounding without more information.

I don't do much with small embedded machines but I would expect standard droop control will be very workable against a large and stiff utility connection. Again it depends on where the machines parallel - if they share an LV bar then they will have more influence over each other because they are effectively decoupled from the utility by the transformer impedance. If they have no common coupling until the 69kV level then they will have virtually no interaction.


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Sometimes I wake up Grumpy.
Other times I just let her sleep!