1- Introduction to Power Quality problems
2- Terms
3- TVSS Installation.

1-Introduction

Power quality issues have always existed. Quality issues were not as important 50 years ago when electrical equipment was not very sensitive to these variations.
Today's houses and business have sensitive microprocessor-based equipment like TV's, stereo's, microwave ovens, computers, fax, programmable controllers and variable frequency motor drives. These types of equipment can be damaged by power disturbances. How many times have you had a piece of manufacturing equipment crash or loose it's programming or a PC lock up and blamed it on good old Bill's operating system, it may have been caused by a power quality problem.

Disturbances can be categorized into four groups.
Noise, Variations, Transients and Interruptions.

Noise is usually caused by interference from a poorly made appliance that is not shielded or is not properly grounded or possibly defective. How many times were you trying to watch a hockey game and someone was using a hair dryer, drill or vacuum cleaner and you would get noise on the screen of your favorite large screen TV. This noise was induced in the electrical wiring ( See Diagram 1) of your house and being picked up thru the power supply. A PLC lost it's programming due to a welder being used by the maintenance department fixing a broken mounting pad on a tool. These types of noise can affect the operation of sensitive electronic equipment.

Variations can last a few milliseconds or longer. These are also called brownouts, swells or sags. Large loads, like an air compressor starting up or elevator motor or even the compressor in your home refrigerator, usually cause these. You may notice the lights dim or get brighter. These types of disturbances will affect sensitive electronic devices.

Transients: Diagram 2

Transients or spikes (See Diagram 2) are very short in duration but are very damaging to sensitive electrical equipment. The voltage on the line can rise to several thousand volts on a 120 Vac home system. Transients can come from the outside world or from the inside houses and offices. Lightning storms or Hydro Line switching are two major causes of outside transients but inside spikes are more common. Refrigerators, washing machines or air conditioners starting up are the most common causes of transients generated inside homes. Location of TVSS Protection must be considered for both sources of transients. Planning of circuits can reduce the chances of transients on sensitive circuits. The Canadian Electrical Code specifies that some loads be on dedicated circuits like refrigerators and freezers and air conditioners. Why share the same circuit with an appliance that is known to create transients with the sensitive devices.

Interruptions are power failures caused by storms, equipment breakdown etc.
Rural areas are more susceptible to interruptions because of the distance away from switching stations. During most strong windstorm power can be lost from tree limbs falling on a power line. TVSS devices won't help you in this situation; a home generator is a common back up device.

2- Common Terms

TVSS = Transient Voltage Surge Suppressor

MOV's = Metal Oxide Varistor

Parallel = A parallel circuit is one in which the component or element is
connected between the lines instead of in the line. TVSS devices are connected between the lines and do not conduct the steady state current of the power line. The suppressor only becomes part of the circuit when suppressing a transient

Wye (Y) = Wye is the description of the power system powered by a transformer in which the windings are connected at a common point (the center point of the Y) which point is also the originating point for the neutral connection. A Wye system always has a neutral

Delta = Delta is the description of the power system powered by a transformer in which the windings of a three-phase transformer are connected in series for a closed circuit as in a triangle.

Transient =Transients are a rapid change in voltage reaching amplitudes in excess of 400 volts and often reaching amplitudes of tens of thousands of volts. Transients rise to peak amplitudes in just a few microseconds and have a total duration of no longer than a few milliseconds.

Spike = Also referred to as impulses or transients, they are high voltage conditions that typically last for a very short duration.

Surge = While improperly used to describe transients, the term "surge" is correctly used to describe long-term over voltages. A surge is an increase in the steady state voltage of the power line and may last from just a few cycles to several seconds or minutes

Noise = High frequency, low voltage oscillations of voltage superimposed on the sine wave, which can disturb the operation of microprocessor based equipment.

3-Installation

There are three categories or physical locations to install TVSS devices.
Category C is outside the building or at the service entrance.
Category B is on a distribution panel or splitter thought or bus system.
Category A is at point of use like power bars or surge receptacles.

Protection from outside and inside generated transients can be achieved by installing a TVSS device at the panel (C or B) and a point of use (A). If a large load internally causes a transient, a TVSS device at an entrance panel (B or C) won't protect your sensitive electrical equipment at point of use (A).

A TVSS unit can be installed directly on the sides or top/bottom of a standard breaker panel. A 2 Pole 30A spare breaker is required to feed the TVSS unit. The breaker is used as a disconnecting mean for the TVSS. The TVSS unit is hooked up in parallel and protects any device or circuit downstream from that location from external generated transients. Mounting the TVSS as close as possible and keeping the hookup leads to a minimum will improve the performance and clamping voltages. The wires must be installed neatly.