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Power Systems

Introduction

What is a power system? In order, to understand a power system we need to understand the different types of power system and the different topologies that are available. A power system is of two types –

  • WYE Power System

  • DELTA Power System

WYE Power System

The WYE power system generally has the neutral grounded giving you a dual voltage system, which are ground fault protected and the neutral reference many drive systems required for operation. The phase voltages are balanced to ground unless the neutral is disconnected or not hooked up. If the neutral is not connected the system can no longer be used as a dual voltage power system. This could result in phase voltages becoming unstable. Transient voltages can cause severe damage to the insulation systems of all the equipment connected to it. WYE power systems cannot and do not filter out the harmonic noise caused by the controls and drives they are powering.

DELTA Power System

The DELTA power system is generally not grounded with an intentional ground connection at the power transformer so the ground current level is very low with the first ground fault. It can operate quite nicely with one phase solidly grounded. It is a natural harmonic filter and can feed surge current when necessary with less line voltage fluctuation. The DELTA power system has been the workhorse of the industry for years but it also has draw backs: Phase voltages can become unbalanced to ground for many reasons, there is no neutral reference required by some drive manufacturers, and the second ground causes a phase to phase fault through ground. Transient voltage events cause high voltage stress on the insulation systems on all of the equipment.

Different Topologies

There are some 11 odd 3-Phase transformer connections but the 4 main types are DELTA-WYE, DELTA-DELTA, WYE-DELTA, and WYE-WYE. Each connection has advantages except the WYE-WYE.

DELTA-WYE: (Isolation Transformer) the primary acts as a harmonic filter by circulating currents through the phases. The secondary with a properly grounded neutral, operates single phase and three phase loads, provides dual voltages, is ground fault protected and the phase voltages are solidly ground referenced.

The DELTA-WYE is very popular in office buildings but has serious limitations in most industrial facilities, as the secondary is very susceptible to harmonics. The primary-secondary phase shift is 210 degrees.

DELTA-DELTA: (Isolation Transformer) the primary as well as the secondary can dissipate harmonic noise, can run “open delta” with only two transformers either by design or in an emergency. The primary and secondary coils of the bad phase can simply be disconnected and run most (58%) of the original 3-Phase transformer bank capacity. This has been the workhorse of industry as production can continue even with one phase solidly grounded and maintenance can locate and repair during non-production times.

WYE-DELTA: (Isolation Transformer) the primary is solidly ground referenced for phase voltage stability and the secondary dissipates harmonics and it can operate with one phase solidly grounded. The WYE-DELTA transformer can operate “open-WYE/open DELTA” with only two transformers either by design or in an emergency. The primary and secondary coils of the bad phase can simply be disconnected and run most (58%) of the original 3-Phase transformer bank capacity. The Primary-Secondary phase shift is 210 degrees.

WYE-WYE: (No Isolation, the worst of the worst) the primary and secondary coils are normally both grounded and some are supplied with an integral ground common to the primary and secondary. All nature’s noise and the noise of all your neighbors will enter your facility unimpeded to every machine, drive and control as it is directly coupled from input to output. Isolation transformers filter low frequency noise by the inductive coupling between primary and secondary and an electrostatic shield can be inserted between the primary winding and the secondary winding to filter high frequency noise that is coupled by capacitive interaction.

The WYE-WYE transformer connection has no filtering and all the noise on your power system is shared. The WYE secondary is very susceptible to harmonics. WYE-WYE systems generate considerable interference with communications systems and some jurisdictions prohibit their use. With the neutral not used or not connected to ground in a WYE-WYE system the phase voltages become unstable and the entire system is susceptible to damage from transient voltage events and the harmonics now travel in the phase conductors. Never try to parallel a WYE transformer with a DELTA transformer as they have a 30-degree phase differential.

Performance

The transformer connection that will perform best in your facility depends on your application. The best for offices and storage facilities is the DELTA-WYE with the neutral solidly grounded. The best transformer connection for heavy 3-Phase industrial applications are the Delta-Delta 3-wire ungrounded. This will give you maximum uptime, the lowest total harmonic distortion (THD) and the most stable line voltages. The addition of Phaseback removes all problems on the Delta secondary.

Downtime an Issue

Nothing costs more than not being able to run your equipment. Downtime costs dollars even when you can’t run your equipment. Equipment needs to be reset or repaired and the level of training for this is increasing at an alarming rate. The costs for replacing electric motors, drives and controllers is very high and rising but it seems that reliability is going the other way. Tooling is damaged or destroyed when a machine controller locks up creating additional expenditures. Add to the rest the costs of downtime for resetting or re-qualifying the machine so it can be returned to production and it is easy to see the need to eliminate these problems.

Power related downtime cost is high, and users cannot afford delays and complication in finding the cause and cure. They simply want to know what to do to fix the problem. The causes of these and other power quality problems are easy to troubleshoot and solve with an understanding of control system operational requirements.

Electric motor over heating can be caused by overload, low voltage (generally caused by a poor power factor), harmonics (voltage and/or current), windings overstressed by transient voltage or current spikes, phase voltage imbalance among others.

The same thing may cause electrical and electronic drive failures. Computer Numerical Controlled machines and other computer controlled machines are also affected by the same things. There are many other variables that will cause machine downtime, but problems eliminated or reset to default state by powering the machine down and up again are generally power related.

Potential Solution

Applied Energy has introduced cost effective solutions to such power related issues that are simple to apply and eliminate the problems. Applied Energy had developed a method to stabilize the phase voltages in ungrounded DELTA and WYE power systems by employing unique electromagnetic suppression techniques. These techniques deal with noise or control problems by prevention and suppression. There are servo stabilizers that can provide phase correction but such stabilizers are limited to only providing phase correction whereas Phaseback can also provide harmonic filtering.

Low voltage conditions caused by overload and poor power factor can simply be solved by connecting a power factor correction capacitor to the motor controller of the larger electric motors not operated by adjustable speed drive controllers. By properly sizing and connecting the power factor correction capacitors the electric motors will draw about 10% less amps than they did before. This can free up system capacity or simply lighten the load on the power system. Lower amps equate directly to the bottom line in efficiency, power loss and system voltage stability.

Harmonic noise on the phase conductors, attempt to make electric motors run at many speeds at the same time causing heat and inefficient operation. This can also cause heat and overload on transformers and other inductors.

In ungrounded power systems the Phaseback EMTVSS filters out harmonics, balances phase voltage to ground, establishes the neutral reference required by many drive control systems, filters out and prevents transient voltage spikes by converting noise energy from all these anomalies safely to heat. The EMTVSS is always online, has no solid-state components to degrade over time, and only one is required per power transformer, not one per sensitive load. Electrical equipment has shorter life due to electrical spikes and noise that result in equipment damage. All electrical equipment connected to a power system protected by Phaseback is likely to have a longer life cycle.

Applied Energy is developing an ungrounded WYE Phaseback EMTVSS with patent protection filed for. This unit can stabilize the phase voltages and filter phase voltage and current harmonics. It also acts as a filter for line voltage and current harmonics. Applied Energy is planning to introduce Phaseback for grounded WYE power systems and a single-phase version of Phaseback for filtering noise and preventing transients.


 


   
 

 

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