What is a constant voltage power conditioner?

Although a constant voltage power conditioner (sometimes referred to as constant voltage transformer or voltage regulator) is a transformer like device, its design and function are totally different. The function of a constant voltage power conditioner is to provide a voltage across its secondary terminals within a specified tolerance (usually ±5%) as long as the voltage impressed on the primary is within the specified bandwidth (usually +10% to -20%). Please see the Power Conditioner Section for more information.

What are the differences between Sola power conditioners?

All three of these products use Sola's patented ferroresonant technology. The primary design considerations for the CVS series were voltage stabilization and magnetic isolation. This group provides ±1% output voltage regulation with an input voltage range of +10%/-20% with moderate (1000:1) normal (transverse) noise attenuation.

The MCR series was designed to address both voltage regulation and magnetic isolation. This group offers ±3% output regulation with an input range of +10%/-20% but also offers magnetic isolation for excellent 1,000,000:1 common mode and 1000:1 normal (transverse) mode attenuation.

The MPC series incorporates all of the benefits of the MCR series in addition to exceeding the low leakage current requirements of UL 544 and providing identifiable output receptacles to indicate they are safe for hospital grade use (orange with green triangles).

The iSOLAtron is an isolation transformer with special filtering to provide an extremely clean ground reference. Although it contains some isolation from noise and surges, it does not regulate the input voltage for swell and sag protection as in the CV, MCR and MPC series. The Three Phase power conditioners utilize microprocessor-based tap switching technology to provide ±5% regulation in three phase installations. The CV, MCR and MPC are single phase only.

Are there any special considerations needed when I select a constant voltage power conditioner?

Special consideration must be given to the type of load to be powered (inductive loads need to be sized to start up currents), load power factor, ambient temperature and where the unit will be installed.

How reliable is ferroresonant technology?

The MTBF (mean time between failures as measured in accordance with Mil. Std 217E) ranges from 10 to 25 years, depending on the model, with typical life being approximately 50 years. All Sola Constant Voltage Power Conditioners are backed by our exclusive 10 + 2 warranty.

Is there any problem with phase shift between the input and output voltages of constant voltage power conditioners (CVPC)?

The phase difference which exists between input and output voltages is in the range of 120 degrees to 140 degrees at full load. This phase differences varies with the magnitude and power factor of the load, and to a lesser extent, with changes in line voltage and load power factor.

We have experienced some temperature problems with other makes of power conditioners. Has Sola addressed this problem?

Sola's ferroresonant power conditioners are very stable with respect to temperature. The change in output voltage is only 0.025% per degree centigrade. Units are factory adjusted to +2%/-0% of nominal, with full load and nominal input voltage. This adjustment to the high side of nominal is to compensate for the natural temperature drift of about 1% that takes place during initial turn on or warm up. When the unit warms up to operating temperature, the voltage typically falls about 1%. This is why no load "cold steel" voltage measurements may be slightly on the high side. At a stable operating temperature, the output voltage will change slightly with varying ambient temperatures. This shift is equal to approximately 1% for each 40C of temperature change. The normal maximum temperature rise of a Sola power conditioner may fall anywhere in the range of 40C to 110C depending on the type and rating. The nominal design ambient rage is between -20C and +50C. (-20C to +40C for 70 to 1000 VA, 60 Hz portable models.)

Are there different constant voltage power conditioner designs?

Yes, there are two basic design concepts. A tap switching design utilizes an electronic circuit along with a traditional transformer core and coil assembly to control the output voltage. As a result, the output voltage tends to be a stepped waveform rather than a smooth sinewave. A ferroresonant design utilizes the electromagnetic induction principle exclusively to produce the desired output voltage. Consequently, the output voltage waveform is a smooth sinewave. The ferroresonant design attenuates transient electrical noise, provides surge suppression per ANSI/IEEE Standards and provides a harmonic free output. These important benefits are not always available with other designs.

Should I use a constant voltage power conditioner instead of a UPS?

Your question involves two different technologies used for differing reasons. 95% of all power quality problems are caused by transient noise, voltage surges, harmonics or frequently changing voltage conditions. Ferroresonant power conditioners provide the solutions for most all of these power quality problems. The primary function of any uninterruptible power supply (UPS) is to provide an alternative voltage source (batteries) to a critical load for some period of time should a complete a power failure occur. Complete power failures account for less than 5% of all power quality problems. For the other 95% of all power quality problems, unless the UPS is the on-line version, the UPS is of no help.

How about response time? Will constant voltage power conditioners work as well as other AC regulator types?

An important advantage of Sola's ferroresonant CVPC is its exceedingly fast response time, compared with other types of AC regulators. Transient changes in supply voltage are usually corrected within 1-1/2 cycles or less; the output voltage will not fluctuate more than a few percent, even during this interval.

Can single phase transformers be banked together for three phase operation?

Yes, this is a common application. Standard configurations include delta-wye and delta-delta connections. Advantages to banking single phase units are:

• They are normally available from local stocks.
• Offer greater application flexibility.
• In the event of a failure of one unit in a delta-delta connection, the other transformers can be made to operate in open delta service at 57% of normal bank capacity.

While banking two or three single phase transformers in a three phase bank is often expedient, it is more expensive than using one Three Phase Transformer.

What are voltage adjustment taps?

In many instances, the supply voltage delivered to the input (primary) of the transformer does not exactly match the voltage rating described. If this happens, the output (secondary) voltage will vary from its nameplate rating because the transformer turns ratio (voltage ratio) is fixed by design. During design and manufacture of the transformer, additional terminations are added to the primary winding to slightly alter the turns ratio. By closely matching the voltage being applied to the appropriate tap, a desirable output voltage can be obtained. Taps are typically located on the primary winding to correct for either sustained high or low voltage conditions on the source. Taps are expressed as a percentage of the nameplate voltage and are designated as FCAN (full capacity above normal) or FCBN (full capacity below normal).

How and why is grounding of transformers important?

Grounding removes static charges that accumulate within a transformer. Grounding also reduces the chance of static discharge causing personal harm and possible equipment damage should the transformer windings accidentally come in contact with the core or enclosure. The actual method of grounding a transformer is simple, defined in NEMA Publication No. ST20, Part 1, Page 4:

"ST20-1 19 GROUNDED Grounded means connected to earth or to some extended conducting body which serves instead of the earth, whether the connection is intentional or accidental. Effectively grounded means grounded through a grounding connection of sufficiently low impedance that fault grounds which may occur cannot build up voltages in excess of established limits"

Before grounding, make sure all contact surfaces are clean and free of any non-conductive protective coating. Any surface where connections are made must be free of rust, scale and any impediments. Make sure the flexible grounding jumper between the core and coil assembly and case is intact and tight. The Metal Enclosure, or frame, of any transformer connected to a circuit operating at more than 30 Volts to ground must be effectively grounded. A grounding conductor for the transformer will have a current carrying capacity in accordance with either the National Electric Code or the National Electrical Safety Code. Make sure grounding or bonding meets NEC and local codes. For further information on grounding, refer to ANSI C1 and C2, NEC 1993 Article 250 and NEMA ST20. These publications go into greater detail concerning grounding than space permits here.

What is balanced loading and why is it important?

Balancing transformer loads means being sure the transformer winding directly feeding a load is not overloaded beyond its capacity. Most single phase transformer applications involve secondary windings rated for 120/240 Volts. These are frequently connected for three wire service. Since the transformer has two 120 volt secondary windings, each one is capable of supplying only one-half of the transformer's rated KVA capacity. If care is not taken, it is possible to apply a combination of 120 and 240 volt loads that will, while not exceeding the total nameplate rating, exceed the rating of one of the 120 Volt windings.

The same is true of three phase transformers, especially those with 208Y/120 Volt or 480Y/277 Volt secondaries. Remember, each of the three secondary windings of a three phase transformer has a maximum capacity of one-third the nameplate KVA rating. It is always necessary to distribute the single and three phase loads as evenly as possible across the three secondary windings without exceeding their capacity.

What are the UL enclosure types?

Underwriters Laboratories adopted a system for rating transformer enclosures which differs somewhat from the NEMA system. The UL system lists just three enclosure types. A UL Type 1 enclosure is intended for indoor service and offers a degree of protection from contact with the device inside the enclosure. UL Type 2 enclosures are also intended for indoor service and provide protection of the equipment inside the enclosure from limited amounts of falling dirt and water. UL Type 3R enclosures can be used either indoors or outdoors and provide protection against rain, sleet, snow and ice formation. The proper UL enclosure rating is listed on the transformer nameplate.

Can 60 Hz transformers be used on 50 Hz?

Yes. 60 Hz transformers can be used on 50 Hz if special precautions are taken. The change in frequency will impact the flux density of the transformer causing it to run hot, as if it were overloaded. To offset this effect, you must decrease the input voltage by approximately 17% (1/6th). This means that a transformer rated for a 480 Volt, 60 Hz input could run at 50 Hz but with a maximum input voltage of 398 volts. On the other hand, 50 Hz transformers can be run on 60 Hz with no ill effects.

What is a NEC Class 2 Power Supply?

A Class 2 power supply is defined by article 725.41 of the National Electrical Code (NEC codebook), and has limited output power. This makes this type of supply useful for wiring in circuits which have less restrictions than if the supply did not meet this rating.

Can a single-phase transformer be connected to a three-phase source?

Yes, the transformer output will be single phase. By connecting two wires from the source (three or four wire) to the transformers primary leads. Care must be used to ensure transformer loading does not create a phase imbalance on the source.

Can transformers be reverse connected?

All dry type transformers can be reverse connected without a derating of KVA size, with certain limitations. All Sola/Hevi-Duty three-phase transformers, and all single-phase transformers rated at 1 KVA and above can be reverse connected without any loss in KVA rating. This is allowed due to the turns ratio and the voltage ratio being equal. Sola/Hevi-Duty does not recommend reverse connecting single phase transformers less than 1 KVA since the turns ratio compensation on the low voltage winding will provide voltages lower than name plate voltage. This voltage will be lower for lower KVA sizes.

Can transformers be operated at voltages other than nameplate voltages?

In some cases transformers may be operated at voltages less than nameplate voltage. In no case should a transformer be operated at a voltage above nameplate voltage unless taps are provided for this purpose. When operating below nameplate voltage the KVA rating of the transformer is reduced due to the increase in current. For example a 10 KVA 480-240 transformer can have a secondary load of 41.6 amps, if the same transformer was operated at 240-120 the same current draw of 41.6 amps equates to a 5 KVA transformer.

How do I determine the correct overcurrent (primary) protection for a 600 Volt class transformer?

Primary Overcurrent Protection
A transformer has all the same component parts as a motor, and like a motor, exhibits an inrush when energized. This inrush current is dependent upon where in the sine wave the transformer was last turned off in relation to the point of the sinewave you are when you energize the transformer. Although transformer inrush could run up to 30 to 35 times full load current under no load, it typically is the same as a motor, about 6 to 8 times normal running current. For this reason it is important to use a dual element slow blow typ fuse - the same type of fuse you would use with a motor. If the time delay is not sufficient, you may experience "nuisance tripping" - a condition where the breaker trips when energizing the transformer but when you try it again, it works fine.

Secondary Overcurrent Protection
Overcurrent devices are used between the output terminal of the transformer and the load for three reasons:

1. Protect the transformer from load electrical anomalies.
2. Since short circuit current is minimized, a smaller gauge wire may be used between the transformer and the load.
3. Per NEC, a larger primary fuse may be used to reduce nuisance tripping.

What is a Buck-Boost transformer and why is it used?

Isolation transformers have separate primary and secondary windings, electrically insulated and isolated from one another. With a relatively high voltage primary (typically 120, 240 or 480 Volts) and a relatively low voltage secondary (typically 12, 16, 24, 32 or 48 Volts), buck-boost transformers are designed to be field connected as autotransformers. These are transformers with one continuous winding, a portion of which is jointly shared be tween the input and the output. No electrical isolation is present in an au totrans form er.

Buck-Boost transformers have two major uses:

1. When field connected as an autotransformer, they can be used to Buck (lower) or Boost (raise) available line voltage in the range of 5 to 27% and at a KVA rating many times that listed on the transformer nameplate.
2. When left as an isolation transformer, they can be used to supply power to low voltage circuits at the name plate rating listed.

What are the application limitations with Buck-Boost transformers?

• A Buck-Boost transformer cannot be used to develop a three phase, four wire wye circuit from a three phase, three wire delta circuit.
• Buck-Boost transformers cannot be used in a closed delta connection.
• Buck-Boost transformers should not be used to correct for voltage drop on a long circuit run where the load fluctuates.
• Buck-Boost transformers cannot be used to create a 240/120 Volt, single phase service from a 208Y/120 Volt three phase supply.