Control.com - Nerds in Control

1. Harmonics and KVAr: is there any relation?

2. KVAr producing because of generation or depends on various load?

3. Generation side if KVAr increases winding will damage?

In my experience existing system.

DG Rated KW - 3500 QTY - 2 - Parallel operation.

We have 5 quay cranes on load side connected with common bus. Normally our erratic load variation each engine 300 to 2000 KW depends on the operation. During this period KVAr variation DG to DG we got more differences, like one engine 300 KVAr and other -2500 KVAr simultaneously P.F. also. We have only option to adjust the Excitation field. Now adjustment also crossed the limits. Is there any other option to control this unbalance. Please give me the clarification about KVAr compensation details.

Note:

1. At present we touched exitation field Manual pot and AVR.

2. Load type inductive (AC and DC motors)

If any manual is available please send it to this mail ID: electwar @ gmail. com

How does this request differ from your previous request?

http://www.control.com/thread.php?id=1026245416

Have you consulted the diesel governor, generator and exciter manuals of the DG manufacturer?

I believe the reason you haven't received a response to your first request was that we don't understand what kind of harmonics you are referring to? Frequency harmonics? Load swings, either real or reactive? What do you mean by "harmonics"?

When did this "problem" begin? After some maintenance or repair on the DGs, or ?

In my mind, an "AVR" is kind of a misnomer for many machines, especially any with Manual field voltage adjustment(s). I even think AVR (Automatic Voltage Regulator) is the name for a particular manufacturer's exciter regulator, but that's only something I was told a long time ago. Many exciter regulators can operate in Manual (or DC) mode, or Automatic (or AC) mode, but not usually both. Depending on the design of the exciter regulator, an adjustment to the Manual pot may or may not affect the Automatic setting/operation. We don't know enough about the exciter regulators at your site.

We also don't know enough about the layout of the site: Are the DGs connected together on a common bus (in other words, are they *not* separated fy transformer(s))? Is one of the diesels operating in Isoch mode and the other in Droop mode or are is there some kind of Isoch droop sharing or some kind of special multi-unit Droop speed control? How is the frequency controlled when the two generators are supplying the load? Are these generators the only source of power for the quay cranes? Is there any kind of tie with a utility or some other source of electrical power?

When you say the load is AC induction motors and DC motors, aren't the DC motors controlled by some kind of electronic DC drive control mechanism (constant voltage or variable voltage)? Don't these use some kind of "dynamic braking" which pumps current back onto the AC "bus" for braking? How does this affect the loading, real- and reactive? Do any of the AC motors use variable frequency drives (which is very common on many quay cranes)?

It's been my experience on shipboard applications with multiple synchronous (AC) generators connected to a common bus with no impedance (transformer) separating them that the operators had to manually adjust excitation depending on loading. If the load was fairly stable, then a change in the excitation of one generator affected it's VAr flow/power factor *and* it had an almost equal and opposite effect on the other generator (if only two generators were synchronized with each other at the time). There was some adjustment on the exciter regulator controls which was referred to in the manufacturer's instruction book as "reactive current compensation" and also as "reactive droop" (that should start some more interesting discussions). The reactive current compensation circuit of each exciter regulator uses an input from a CT (current transformer) which is monitoring the generator output.

When the load is finite (as I would consider it to be in this case: the load is the sum of all the motors and lights in operation on the cranes, even if they are varying they shouldn't exceed the capacity of the DGs) and the reactive load is finite (because the number of motors and equipment is fixed and their reactive load, even if it varies slightly because of some of the components, can't exceed a certain value), a change in the output of one generator will have a nearly equal and opposite effect on the other generator. For example, presume one of the generators is operating in Isoch mode, or the Isoch load sharing module is configured such that one of the units is deemed to be the primary unit. If the real load (watts) of the system is relatively stable and someone manually increases the real power output (watts) of the secondary unit, the output of the Isoch/primary unit will have to decrease in order to maintain the frequency setpoint; if it didn't, the frequency of the system would increase. A change in the power output of one of the units will either cause the other unit to change its output proportionally to maintain frequency, or the frequency will vary from setpoint (because the real load hasn't changed).

Likewise, if the reactive load of the system were stable and someone increased the reactive output of one unit, the reactive load of the other unit should decrease. Increasing the reactive VAr flow from one unit will mean the VAr flow of the other unit should decrease proportionally (because the VAr load of the system hasn't changed). Most exciter regulators just adjust excitation to control terminal voltage; some other control means monitors VArs/power factor and adjusts excitation as required.

Again, except for the harmonic thing which isn't clear, I think you should find most of the information in the manufacturer's instruction book(s) for how to adjust the exciter regulator. Most of the exciter regulators I have worked on didn't work correctly when Manual adjustment were made while the regulator was operating in Automatic. I don't have a lot of experience with small "island" loads like this with multiple generators and some kind of electronic DC drive(s) and how they might affect operation. My shipboard experience tells me that when loads are being moved, it's not uncommon for frequency, voltage and power factor to swing in proportion to the motor(s) being used to move the load and the magnitude of the load of each motor.

So, it's not clear if you're trying to make the generators have a constant power factor/VAr flow, or what. Because I don't think it can happen if my interpretation of your site is even remotely correct. When the loads are varying, as they will when moving cargo with quay cranes, the load (real and reactive) isn't going to be constant. A good Isoch control on one unit, or a good Isoch load sharing system, would handle the frequency variations. A properly adjusted exciter regulator should be able to handle the reactive variations, and, again, what those would look like with DC drives and/or dynamic braking would be very interesting, indeed. Not impossible, but interesting to observe and try to tune for.

One of the problems I encounter quite a lot is that of perception: Someone believes this or that *should* or *should not* be happening based on their understanding of the system. When, in fact, this or that cannot happen or should happen. Based on the questions, I'm wondering if that's what we're dealing with here? Under the situation when loads (real and reactive) are varying on a finite bus such as I would consider your application to be, it's not clear what condition/situation one should be tuning for. Worst case? "Medium" load? "Light" load? Real power or reactive pow__? (I *ALMOST* said it! Google "power triangle" or, again, almost any text or manual one looks at, they all refer to reactive pow-er. But, we can't use the un-hyphenated version of that word here.)

I really think you need a qualified technician to come and visit your site to observe what's occurring and what should or should not be occurring, and then help with tuning, as appropriate.