LV Blowers & Compressors Stopped During 33kv Incoming Dips

One wouldn't expect plant of this size to "ride through" a brown-out without some sort of flywheel effect in the equipment.

If the starters for the equipment are required to maintain functionality through the brown-out then some form of uninterruptible power supply facility needs to be added to sustain the contactors through the brown-out, however the plant will start on its own once the brown-out has cleared and the facility may not want that.

The VSDs are behaving as they ought to: await restart after power loss.

Repairing the 33kV supply to prevent recurrence is extremely attractive. One might be able to put pressure on the utility supplier to improve through the commercial arrangements in place between that body and the user.

What's the question?

What is possible reasons some blowers & blowers are continuous working and some did not as they are same power source and same configuration.

It could be as simple as the tolerance of the coils for electromechanical contactors, maybe some dirt on the face of the laminations that make up the magnetic circuit, or subtle differences in design of the circuits, tolerance of capacitors is often wide. The location of each piece of equipment within the distribution system, where it is connected in relation to other components, could create small voltage differences enough to allow some equipment to maintain, while other drops out.

Without an extremely detailed analysis of all of the components connected in the system, between the equipment that rides through and the equipment that doesn't, I don't think you will be able to come up with just one or two causes for your observation.

In power stations, we used to have timer included in the motor stater circuits for all essential drives. The timer is off-delay type and maintains 'close' contact in the power contactor closing circuit (DOL) for 2s. This used to ensure that the subject pump / compressor restarts automatically in case the power is restored to healthy levels within the set time.

In O&G stations, these motors are provided two stage restart scheme.

One, is set for 0.2s and all the drives (essential as well as normal) are allowed to restart immediately and automatically in case the power is restored to healthy levels within 200ms.

The second is only for identified / essential drives and the restart is through a set time delay (if the power is restored after 200ms). This is staggered starting to prevent sudden overloading of incoming power transformer if large no. of drives are to start simultaneously.

May be, your plant requires one such restart scheme.

The ABB drives are designed to drop out with a low voltage event. They are doing what they need to do, to protect themselves.

The voltage dip is it an inside the plant event or from the utility.

If it is an inside the plant event, you are looking for loose connections or overloaded equipment. You stated that you have motor loads that are 90% of the rating of the transformer. Something that is not very big can put the transformer beyond it's design limits. The age of the distribution system is also a factor. When was the last time the maintenance group went through and verified all the connections.

Remember, "If you did not document it, you did not do it"

Good luck.

A data logger might provide additional information.