Power Systems

Published: 23 Feb 2004

By Vishal Sapru, Research Analyst, Frost & Sullivan

Daniel Princinsky, President, Applied Energy LLC


In order, to understand the capabilities of a power system, we need to understand the different types of power systems and the different topologies that are available. A power system can be manufactured in two types:

  • WYE Power System
  • DELTA Power System

WYE Power System

The WYE power system generally offers neutral grounding giving the user a dual voltage system which is ground fault protected and the neutral reference many drive systems required for operation. The phase voltages are balanced to ground level unless the neutral is not hooked up and/or disconnected. 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 level so the ground current level is very low with the first ground fault. It can operate smoothly with one phase solidly grounded. It is a natural harmonic filter and can feed surge current when necessary with less line voltage fluctuations. The DELTA power system design has been the workhorse of the industry for years, but it also has its 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 of all of the equipment.

Different Topologies

There are approximately eleven 3-Phase transformer power system connections but the four main types are DELTA-WYE, DELTA-DELTA, WYE-DELTA, and WYE-WYE. Each connection has unique advantages except for the WYE-WYE.

DELTA-WYE: (Isolation Transformer) the primary winding acts as a harmonic filter by circulating currents through the phases. The secondary winding 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 winding 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 in most (58 percent) of the original 3-Phase transformer bank capacity. This has been the workhorse of the industry as production activities can continue even with one phase solidly grounded and required maintenance can locate and repair during non-production times.

WYE-DELTA: (Isolation Transformer) the primary winding is solidly ground referenced for phase voltage stability and the secondary winding dissipates harmonics. This design 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 in most (58 percent) of the original 3-Phase transformer bank capacity. The Primary-Secondary phase shift is 210 degrees.

WYE-WYE: (No Isolation, least secure design) the primary and secondary coils are normally both grounded and some are supplied with an integral ground common to the primary and secondary. Environmental noise and background noise will enter the users facility unimpeded to every machine, drive and control as it is directly coupled from input to output.

An isolation transformer filters 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. It is best to never try and parallel a WYE transformer with a DELTA transformer because they have a 30-degree phase differential.


The transformer connection that will perform best in your facility depends on your application. DELTA-WYE is best suited for officies and storage facilities with the neutral solidly grounded. The best transformer connection for heavy 3-Phase industrial applications is the DELTA-DELTA 3-wire ungrounded. This will give the user 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 is an Issue

Nothing costs more than not being able to run equipment smoothly and reliably. Downtime costs dollars when the user cannot run their equipment. Equipment needs to be reset or repaired, and the level of training for this is increasing at an alarming rate. The cost of replacing electric motors, drives and controllers is very high, but reliability is decreasing day by day. Power related downtime cost is high, and users cannot afford delays and complication in finding the cause and cure. They are hard pressed to identify and fix the problem. The causes of these and other power quality problems are easy to troubleshoot and solved better with the 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 attributes 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 EMTVSS

Applied Energy has introduced a cost effective solution to such power related issues. 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 other servo stabilizers available that can provide phase correction, but such stabilizers are limited to only providing phase correction. Applied Energy's Phaseback technology provides the phase correction in addition to 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 percent 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.

Applied Energy is developing a patent pending ungrounded WYE system called Phaseback EMTVSS (electromagnetic transient voltage surge suppressor). 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 the Phaseback product for grounded WYE power systems and also a single-phase version of the Phaseback EMTVSS for filtering noise and stabilizing and balancing voltages.

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.


In today's high-tech competitive business environment a power related disturbance can result in losses worth billions of dollars in production and could potentially result in the damage of the plant. With power quality comes issues such as, harmonics, transients, surges, spkies among others. These are issues which need to be dealt with before the equipment gets damaged. Multiple power quality products are available which try to suppress unwanted power quality relates issues. Applied Energy has developed a Phaseback EMTVSS which acts like a surge suppressor, harmonic filter and a voltage regulator thus providing protection from to the equipment and the facility from unwanted power quality issues. The Phaseback EMTVSS filters out harmonics and balances phase voltage to ground. It filters and prevents transient voltage spikes by converting noise from all these anomalies safely to heat. This is a product to look out for in the coming years.

For more information regarding Applied Energy and its technology, please contact Dan at dan@applied-energy.us

For more information regarding Frost & Sullivan power quality equipment research, please contact Vishal at vsapru@frost.com

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