Hello everyone, I'm currently facing a challenging situation with my boss regarding our electrical setup for a critical project. Whenever I attempt to express my concerns about our system, he dismisses my input as uninformed. I'm reaching out for guidance to ensure we're on the right track. If I can validate my thoughts during this process, that would be a bonus. In our facility, we have a 208V three-phase ungrounded delta transformer supplying power. We're in the process of developing custom manufacturing machines that require an output of 480V three-phase. Therefore, it's imperative that we use a transformer to step up the voltage. I've calculated the total Full Load Amperage (FLA) for all the servo motors in this machine, which amounts to approximately 116 amps of three-phase 480V. The issue arises because my boss purchased a used delta-wye transformer that's configured as a step-down transformer. He mistakenly wired it in reverse; the 208V three-phase is sent to the wye secondary, which should provide 480V at the primary while corner grounding the delta at H3. Upon measuring the incoming L1 from the transformer to ground, I found it to be nearly zero volts (0.05 VAC), while L2 and L3 both read 480 VAC. Measurements between any two lines yield 480 VAC. However, I started receiving error messages on my Kinetix 5000 series servo controllers, which I had never experienced before. With assistance from my local distributor, we've determined that we're likely missing a phase due to the corner grounding of the delta configuration. This misconfiguration may be causing problems with the pre-charge amplifier in the Kinetix system. The distributor has recommended replacing the transformer with a Delta/Wye step-up or boost transformer for better performance. When I informed my boss about the single phasing issue and the need for a transformer replacement, he reacted defensively, insisting that I didn't know what I was talking about. I could really use some advice from those experienced in this area: 1. Is a corner-grounded delta configuration suitable for automation machinery with sensitive servo drives? 2. By grounding H3, does it effectively cause single phasing between H1 and H2? 3. Is the combination of a 208V three-phase delta primary with a 480V three-phase wye secondary the correct transformer setup for our needs? Thank you for your assistance, and I apologize for the lengthy post!
Experts in the field with far greater knowledge than mine will likely weigh in soon, but I've noticed that most drive manufacturers advise against using a corner-grounded delta configuration. It's a good idea to check your drive manual for any specific guidelines. If it clearly mentions that corner-grounded delta should not be used, be sure to bring this important information to your boss’s attention.
The Kinetix offers an optional grounding screw that can be detached for both the AC and DC bus, allowing for the use of a Corner Grounded Delta configuration. However, this practice is not advised. My primary focus is on the question of phasing and whether the Delta configuration is acceptable for use. I appreciate your confirmation on this matter.
Tim Ryder inquired: 1.) Is using a corner grounded delta configuration suitable for automation machinery that relies on sensitive servo motors? 2.) When grounding H3 at the corner terminal of the delta, does this lead to single phasing for H1 and H2? 3.) Is a 208V 3-phase delta transformer paired with a 480V 3-phase Wye transformer the correct setup? Thank you, everyone, and I apologize for the lengthy post. To provide some insights, I'm not an expert, but here’s what I think: 1) It's not advisable. Most Variable Frequency Drive (VFD) manufacturers either discourage this setup or require the removal of an RFI jumper to prevent potential damage to the RFI filter section. 2) No, grounding one phase may not truly achieve single phasing, but it could potentially mislead the drive into incorrectly sensing a phase loss. 3) For the secondary configuration, that's accurate, but I'm unsure about the optimal primary configuration.
**Subject: Essential Steps for Transformer Upgrade** Hi Tim, Do you truly need to operate all servos simultaneously under full load conditions? Have you considered staggering or offsetting their movements for testing? You mentioned a requirement of 115 amps at 480 VAC in a three-phase system. Performing the calculation—115 amps multiplied by 1.73 and then by 480 results in 95 kVA. This suggests that your load falls between a 75 kVA and a 112 kVA transformer range. If this is indeed your operational necessity at your 208V facility, be prepared for a significant financial investment. It appears that you are an OEM provider catering to industrial clients. Most, if not all, of your customers likely operate on a 480/277 center-bonded voltage system; therefore, it's crucial to conduct your equipment testing at that incoming voltage. As a professional in this field, it's essential to avoid compromising with a corner-ground, three-wire delta 480V setup. If your business aims to supply large systems to industrial users in the long term, establishing a reliable 480/277 wye center-bonded system is imperative. However, if you anticipate only occasional demand for this system, leasing a temporary industrial facility might be a viable option. If you're considering updating your current setup for these requirements, I recommend reaching out to Jae at Power-Tran in Ferndale. His team specializes in creating tailored step-up transformers that convert your three-wire 208V to a four-wire 480/277 wye system. A licensed electrician will ensure that the new transformer’s secondary is bonded in compliance with NEC (NFPA-70) standards. Now, let's assess whether your existing facility has an adequate 208V system. If you choose a 75 kVA step-up, your electrician will need to supply 300 amps to the 208V primary. On the other hand, a 112 kVA upgrade will require 400 amps to be brought to the 208V primary. (Jointly, we often manufacture machinery intended for Europe, which often necessitates procuring transformers and VFDs to deliver 380V or 415V 50Hz power for operation in our 480/277 wye facility.) Best regards, Plastic
An alternative solution, based on your duration and frequency of needing 480 power, is to consider renting a generator set (genset).
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Answer: A1: Using a step-down transformer in reverse for stepping up voltage can lead to improper operation, especially if the transformer is not designed for such configurations. In this case, the corner grounding of the delta may lead to missing phases, affecting sensitive equipment like servo drives.
Answer: A2: A corner-grounded delta configuration is generally not suitable for sensitive automation machinery like servo drives. This setup can cause issues such as single phasing, which can disrupt the operation of systems like the Kinetix 5000 series servo controllers.
Answer: A3: Grounding H3 in a corner-grounded delta setup can lead to single phasing between the other phases (H1 and H2). This can cause voltage imbalances and may result in error messages or malfunctioning of equipment that requires balanced three-phase power.
Answer: A4: For
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