Overvoltage is defined as incoming line voltage at the point of use which is greater than the Public Service Commission’s mandated legal limits; and/or greater than the voltage ratings of the connected equipment. Overvoltage is considered a safety hazard by all industry standards, and can cause premature failure of connected equipment.
Overvoltage has been a widely known industry problem for many years, but it is not generally understood by many who have to deal with it. Power companies have been unable to control it adequately.
Overvoltage occurs most often during severe cold winter weather for the following reasons: (1) Inadequate size of power distribution systems; (2) slow reaction time for power company’s distribution systems to regulate voltage during extreme load variations; and (3) abrupt reductions of loads.
- Inadequate size of power company distribution systems (transformers, power lines, etc.) often cannot provide sufficient power to handle increased loads due to severe cold weather and maintain proper voltage levels. During these periods of time, in order to provide sufficient power to the points of use furthest away from the nodes of distribution, the voltage must be increased by the power companies, sometimes above the allowable limits. Although points of use far away from the distribution nodes may then have proper voltage (due to voltage drop in the undersized lines), the points of use nearer the nodes of distribution often experience overvoltage.
- Slow voltage regulation reaction time during extreme load variations cause voltage regulation “overshoot” which results in overvoltage. The amount of power required for heating is directly proportional to the decrease in outside air temperature. As load changes in a power distribution system, the voltage must be matched to the load, using various methods of voltage regulation, to prevent overvoltage. If the rate of load decrease exceeds the rate of corrective voltage decrease, overvoltage will occur. Peak power loads often occur in the summer. However, during severe cold winter weather, the rates of temperature change are approximately three times greater than during the summer. Therefore, voltage regulation “overshoot” is more likely to occur during severe cold weather and cause overvoltage.
- Abrupt reductions of loads due to power distribution failures occur mostly during periods of extreme winter weather. This is due to damaged distribution systems (downed power lines and transformers, etc.) by winter storms, ice, and snow in a certain parts of a sector. These abrupt decreases then increase voltages in other parts of the sector, often causing overvoltage at the points of use.
Proof of the concentrated occurrence of overvoltage during severe cold weather periods has been particularly evidenced over the past five decades by significant equipment failures, property damage, and repair costs due to overvoltage during the nationwide severe cold winters of 1975-1976, 1980-1981, 1999-2000, and 2009-2010. During and after these periods, numerous product recalls occurred. Redesigns by many manufacturers were made in an attempt to provide equipment that would withstand overvoltage. This rationale is flawed because equipment component voltage ratings need to exceed the current industry voltage tolerance standards in order to withstand overvoltage. As there are many components that are used (or can be used) in a system they all would have to be equally overdesigned. The current safety standards must be adhered to in order to ensure uniformity and safe design, or they must be changed to do so.
Under any standard, the proper approach to overvoltage is to control it or avoid it. Due to the many complex causes and unpredictable situations, it is a foregone conclusion that it cannot be controlled effectively to all points of use at all times by power distribution systems. However it can be controlled at the point of use, by individual voltage regulation devices, for moderate additional costs. It can be avoided by switching it off at the point of use when it is present with the use of lower cost devices.
OPTIONS TO ADDRESS THE ISSUE OF OVERVOLTAGE:
| OPTIONS | COMMENTS |
| Ignore the effects of overvoltage | Unacceptable damage and safety risk |
| Eliminate overvoltage from distribution systems | Impossible, at the present time |
| Control incoming voltage with regulation devices at the point of use | High cost |
| Design all system components to withstand overvoltage | Departure from uniform standards and risk of catastrophic damage and fire |
| Automatic disconnection of equipment when overvoltage is present using non-resettable fuses | Eliminates risk but has problematic “no heat” calls and costs to replace fuses |
| Automatic disconnection of equipment when overvoltage is present and minimize the effects with automatic or manual reset voltage limits | Feasible with minimal additional costs |
| Purchase insurance to cover costs resulting from overvoltage | Available in most home owners policies and from some power companies |
The HVAC industry and all other industries which utilize electrical components are in some way or at sometime affected by overvoltage. Recognizing and understanding it; and making the most adjustments possible to control, reduce or eliminate damages (to equipment and to people) are just the first steps towards eliminating it.
NOTE: Electric heaters are especially affected by overvoltage because they produce substantially more heat than their ratings when subjected to overvoltage; and therefore present a greater concern for safety than most other products in HVAC systems when overvoltage is applied. Ongoing research studies and more than 50 years specializing in providing electric heat for use with most HVAC equipment, Warren Technology is uniquely positioned to evaluate the issue of overvoltage, and to recommend corrective solutions.
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