VFD not reaching 50 Hz

[ootyty]

G'day I have a 9600 series Weiken VFD that we were using in a farm. The VFD incoming was struck with lighting and blow the Full Bridge Rectifier off. I've got it replaced and the drive display and everything was working.

I tried to get the pump to run and it was initially working for maybe 5 minutes before I shut it down.

I then turn it off and try to run the pump again but this time the VFD wont reach 50 Hz (fluctuating around 46-47 Hz) the pump was going crazy with pressure fluctuating between 10-20 kPa (Normally operating at 15 kPa steady @ 50 Hz).

I disconnected the pump and from the VFD display I can see it going up to 50 Hz without the pump connected.

Initially thinking that the pump might be broken I then put the motor on DOL via MCB and the pump runs just fine maintaining 15 kPa.

That leads me to think that the VFD is broken however I've got no idea what else I can check with the VSD does anyone else have similar issue before with any VFD?
I've tried the IGBT testing method but no luck for me. Please help..

 

[kellys_eye]

(Normally operating at 15 kPa steady @ 50 Hz)

then put the motor on DOL via MCB and the pump runs just fine maintaining 15 kPa

errrr... leave it as DOL? I'm sure I'm missing something here

Then again, a lightning strike inevitably (in my marine experience) travels a lot further than you'd expect and damage elsewhere seems probable as the symptoms tell us. Something in the feedback circuitry seems the likely place to start.

 

[Bluejets]

errrr... leave it as DOL? I'm sure I'm missing something here

mmm....me too.
Why use a vfd , especially on a pump where you need constant pressure apparently at full supply as you wrote.
What size motor..?

 

[Delta Prime]

Does your recently replaced & working CNWeiken 9600 series frequency inverter "display," give a fault code?

 

[Bluejets]

Doesn't seem like much pressure ( around 2 lb sq inch) ....likely to get fluctuations around such a small pressure.

 

[ootyty]

Does your recently replaced & working CNWeiken 9600 series frequency inverter "display," give a fault code?

No fault recorded but I did realize that the VSD current is drawing 10% higher than previously.

 

[ootyty]

Doesn't seem like much pressure ( around 2 lb sq inch) ....likely to get fluctuations around such a small pressure.

Yup not a pressure pump, its a submersible pump, we use it mainly because we need to pump up 200m elevation.

 

[ootyty]

errrr... leave it as DOL? I'm sure I'm missing something here

Then again, a lightning strike inevitably (in my marine experience) travels a lot further than you'd expect and damage elsewhere seems probable as the symptoms tell us. Something in the feedback circuitry seems the likely place to start.

The VSD is there mainly as a protection and speed control, at times we need to reduce the pump speed when needed. The intention is that we want to have as much protection as possible for the pump. DOL via MCB have no protection for the pump. Last lighting strike blown off the bridge rectifier in the VSD even though there is a MCB above the VSD, the effect would be worst if its DOL to pump.

 

[ootyty]

More info here:
The pump is 2.2kW 415V 6.1A Submersible pump
VSD 2.2 kW
Main Wiring connection consist off: 3 Phase + 1 Neutral + 1 Earth to control Panel.
Circuit 1 on Control Panel: 3 Phase to MCB (C10) to VSD to Motor + 1 Earth to VSD & Motor
Circuit 2 on Control Panel: 1 Phase + 1 Neutral to 240V MCB (C10) to 240V-24V Power Supply+ 1 Earth

When lighting strikes only Circuit 1 MCB trips and VSD bridge rectifier blown off.
Circuit 2 is entirely fine with no MCB tripping. The main MCB (C40) in our ditribution board also tripped.

That leads us to think that only 1 of the phases got struck by lighting causing the 3 Phase MCB to trip. That was confirmed after tested the blown off bridge rectifier only 1 Phase is shorted. By the way the bridge rectifier was SGBJ2516.
We have also realized our Earth connection on the Control Panel shows sign of oxidation and black mark leading us to suspect there is an Earthing problem. However that is not the concern in this post.

 

[Bluejets]

2 lb sq inch doesn't seem right to me..........(15kPa)
Point being, if that's incorrect, what about the rest..?

 

[Delta Prime]

As you experienced a lightning strike can cause a lack of voltage symmetry in utility power distribution transmission lines.
Terminating at your farms electrical meter, service panel.
ANSI (C84.1) Maximum unbalanced electrical supply voltage must be limited to 3% when measured at the electrical meter of your farm under no load conditions. That means, it is your responsibility to verify the balance voltage conditions measured at the meter of your farm, as stated before, within 3%.
Unbalanced voltages are often caused by system load distributions when lightning strikes a transmission line.
And or large single phase loads, Capacitor Banks faulty power factor corrections. Three phase high current rectifiers and motors.Unbalanced currents flowing in neutral conductors. loose,corroded, pitted connectors or contactors. Even a farm next door or up the road can cause it.
Phase voltage differences causes circulating current in three phase motors Eddy currents. Motors may not reach their rated speed or only reach 75% of the rated horsepower on the name plate. VFD line currents can
Become unbalanced because of excessive currents in one or two phases. Increasing the harmonic
Content of the output current diodes!
As a direct result would account for your VFD fluctuating around 50 Hz.

 

[ootyty]

2 lb sq inch doesn't seem right to me..........(15kPa)
Point being, if that's incorrect, what about the rest..?

Bud, the concern is not how much pressure the system is doing, regardless of whatever pressure it is even if its 1 - 2 kPa its not important, what is important is maintaining of pressure (Gauge needle stays relatively still at designated value when pump is running). The issue is the pump is not operating at its designated pressure ie. High flutuation in pressure reading via the gauge. In laymans term the needle is bouncing left right left right not stationary as it was before when VFD is operating (same goes to VSD struggling to reach 50Hz).

 

[ootyty]

As you experienced a lightning strike can cause a lack of voltage symmetry in utility power distribution transmission lines.
Terminating at your farms electrical meter, service panel.
ANSI (C84.1) Maximum unbalanced electrical supply voltage must be limited to 3% when measured at the electrical meter of your farm under no load conditions. That means, it is your responsibility to verify the balance voltage conditions measured at the meter of your farm, as stated before, within 3%.
Unbalanced voltages are often caused by system load distributions when lightning strikes a transmission line.
And or large single phase loads, Capacitor Banks faulty power factor corrections. Three phase high current rectifiers and motors.Unbalanced currents flowing in neutral conductors. loose,corroded, pitted connectors or contactors. Even a farm next door or up the road can cause it.
Phase voltage differences causes circulating current in three phase motors Eddy currents. Motors may not reach their rated speed or only reach 75% of the rated horsepower on the name plate. VFD line currents can
Become unbalanced because of excessive currents in one or two phases. Increasing the harmonic
Content of the output current diodes!
As a direct result would account for your VFD fluctuating around 50 Hz.

That is very informative thanks for your reply, I have to look further into this as it seems like that could be the case since the voltage from phases-neutral for each phase are quite different the last time I measure (in terms of phase voltage). I've measured voltage-neutral as well and found out that one of the phase-neutral is reading exactly 240V and the rest is a bit higher ~246V, which I assume is a bit low as I remember most of the time the voltage-neutral should be around 250V when measured with multimeter correct me if I'm wrong though as I'm still quite new on actual field troubleshooting.

 

[Bluejets]

Bud, the concern is not how much pressure the system is doing, regardless of whatever pressure it is even if its 1 - 2 kPa its not important, what is important is maintaining of pressure

To begin with, I am not "your Bud".
Keep this trash for your backstreet mates.

Maintaining a pressure of 2lb sq inch will be almost impossible given any variations in supply, loading and delivery friction variations amongst others.