Inrush of Induction Wind Generator

[pajce]

Hi all:
I need to model Induction generator farm. I understand fault current contribution from these generators is very low due to absence of voltage at terminals and consequently flux in the machine core. But I wonder if I should regardless chose Impedances Option. In my modeling software gives me NEMA design that are with LOCKED ROTOR codes that represent ratio of KVA/HP. Would my choice among these matter at all considering I am modeling induction generator (not motor)? I understand generators are usually started up to speed to speed slightly higher then syncfronous rotating field of the utility and then connected to network. Inrush would normally be around 2 times full load (I was told)?
Problem is this inrush does not fit to my inrush options in motor properties tab I use for model.
Any help appreciated.

 

[dpc]

You really need software that provides for direct modeling of an induction generator. Inrush and fault contribution are two different things, anyway.

The induction generator will contribute significant fault current, but not for very long - a few cycles normally. However, if the power factor correction caps stay connected to the generator, the time period could be extended dramatically.

Wind turbine supplier should be asked for information on fault contribution for a typical unit.

 

[waross]

Considering that the first induction generators were induction motors you can probably model the induction generator as a motor for fault studies and get usable results. Note that a motor contribution of symetrical current decays as the motor slows down and if the motor is supplying energy into the fault it will slow down very rapidly. The induction generator will still be driven and will not slow down to the same extent. Model it as a motor with very high inertia.
There will be a voltage drop between the utility source and the fault. Depending on the induction generator's location relative to the source and the fault there may be enough terminal voltage at the induction generator to produce a non decaying current into a fault.
respectfully

 

[pajce]

Waross:
for NEMA motors which design I should chose of these below:

NEMA
Code Letter KVA/HP
with locked rotor
A 0-3.14
B 3.15-3.55
C 3.55-3.99
D 4.0-4.49
E 4.5-4.99
F 5.0-5.59
G 5.6-6.29
H 6.3-7.09
J 7.1-7.99
K 8.0-8.99
L 9.0-9.99
M 10.0-11.19
N 11.2-12.49
P 12.5-13.99
R 14.0-15.99
S 16.0-17.99
T 18.0-19.99
U 20.0-22.39
V 22.4-and up

Design A
has normal starting torque (typically 150-170% of rated) and relatively
high starting current. Breakdown torque is the highest of all NEMA types.
It can handle heavy overloads for a short-duration. Slip <=5%. A typical application is
powering of injection-molding machines.

Design B
is the most numerous type of ac induction motor sold. It has normal starting
torque, similar to Design A, but offers low starting current. Locked rotor torque is
good enough to start many loads encountered in industrial applications. Slip <=5%.
Motor efficiency and full load power factor are comparatively high, contributing to the
popularity of the design. Typical applications include pumps, fans, and machine tools.

Design C
has high starting torque (greater than previous two designs, say 200%), useful for
driving heavy breakaway loads. These motors are intended for operation near full speed
with-out great overloads. Starting current is low. Slip <=5%.

Design D
has high starting torque (highest of all the NEMA motor types).
Starting current and full-load speed are low. High slip values (5-13%) make this motor
suitable for applications with changing loads and attendant sharp changes in motor speed,
such as in machinery with flywheel energy storage. Several design subclasses cover
the rather wide slip range. This motor type is usually considered a 'special order' item.


Thank you.

 

[waross]

I would phone a few manufacturers and ask.
respectfully

 

[jraef]

My experience is that most Induction Generators are Design B as far as the motor characteristics are concerned.

I also doubt your starting current will be that low. From a dead stop you cannot accelerate the motor with the wind alone. You need to accelerate to the slip speed as a motor, then allow the wind to take it over synchronous to become a generator. Typical motoring start current is never less than 350% in my experience (using soft starters).

If you have an inverter on that generator, everything is a whole new ball of wax by the way.

From what I was told by Wind Generator people I worked with, once on-line as a generator in a grid connected system you really need to consider the fault contribution just as if it were any other generator because you don't know if the "prime mover" will in fact disengage.

 

[00123456]

Hi,

Point:-1
I had a experienced with SUZLON ENERGY LTD, it's india's largest wind power generation company (almost 150MW). They are using induction generators of SIEMENS & Jyoti ltd make which are having a dual winding connections (350KW & 500KW). If wind spped is higher then 9kmps then winding connection is on 500KW output & lesser than 9kmps then it' automatically changer over on second winding (350KW) & that condition is called as down coupling condition. During down coupling (500KW to 350KW); we have observed & recorded inrush current (apporx. 10ms to 20ms) because of the momentory motoring action of machine which is some what around 2 times to 2.25 times of rated per machine. Now, normally, induction generators are always connected in groups (may be 10 or 12 genrators connected to one 33kV feeder) that can be increse overall inrush current on feeder. My point of view; you need to consider fault contribution during following conditions;

1) Starting of all motors (why i am writing motor? because initially it's motoring action) connected in groups & 3-Phase fault on feeder/machine termonals.

2) During Down coupling; how many machines are switch over from wdg1 to wdg2 connection & see the fault contribution.

Point:-2
Mr. JRAEF said motor start current is never less than 350% by using soft starter, but our experiences says; if you can use FCMA starters (soft starter) then you can reduced starting current below 350%. We have been installed almost 300 HT motors up to 4MW & used FCMA (Flux. Complem.) starters & recuded starting current from 5 times to 2 times of rated.

Point:-3
Regarding fault contribution time; I have experienced with ETAP Power system & NETPMAC software; normally, simulation shows max. 60ms not more.

Point:-4
Detail Power system studies require by using power system analysis software like ETAP, CYME, EDSA etc.

Thanks

 

[DanDel]

pajce, are you doing hand calculations or using software? If so, which software package are you using?

 

[pajce]

Dan Del: I am using Siemens PSS Adept software.

thanks for all your comments guys. I believe our Utility practise is to kaskade with generators. I am not sure if we allow for start from dead end, or speed up first and then connect to the grid. I would think inrush is not the same for this 2 options. Some documents I got, said inrush is limited to 2 p.u. Again, problem I have is how is this equivqlent to my NEMA motors options given in my software.

regards

 

[ters]

Additional modeling complications can arise if you encounter one of newer European wind generators (such as Enercon) which are sometimes 6 phase nominally 20 Hz units but being also able to operate at variable speeds/frequencies since they are connected to the grid through a 6-phase-rectifier----3phase-inverter coupling.

 

[jraef]

I don't know that Siemens software program, but I used to use SKM and I would have modeled the starting by using a solid state starter set to 200% current limit (if you believe that would work). The Start modeling would/should be the same.

 

[00123456]

As per my knowledge, For two years, ENERCON has introduced Synchronous machines not induction generators. Fault contribution from synchronous machine is differ than induction machine.

Thanks

 

[Bahram7]

I would recommend EMTP-RV (

http://www.emtp.com)

which offers atate-of-the-art modeling of electrical machines. EMTP-RV is currently used in may wind farm simulations around the world in studies related to starting, faults, stability, LVRT, etc.

Bahram7

http://www.Simtech-Intl.com