TSi AC Voltage Regulators

Where should TSi voltage regulators be used?

Soft supply–problematic tap changing in distribution transformers

The TSi voltage regulators should be used in areas of soft (high impedance) supply systems and also in areas where distribution transformer tap changers cannot keep up with the voltage regulation due to peaking demand. Therefore the voltage regulators find application both in rural as well as in metropolitan regions. Under-voltage sags and over-voltage swells are often harmful. Over-voltage can cause burn out (a 10% increase in voltage can cause a 21% increase in power). Under-voltage can cause loss of torque (a 10% decrease can drop motor torque 19%).

Rural areas-SWER supply systems

In many rural areas supply is via single wire earth return (SWER). The SWER supply system can be subject to large voltage regulation. Voltage sags are due to the relatively high line impedance (compared to metropolitan supplies). Voltage swells can be due to the Ferranti effect. The line is then affected when lightly loaded by its capacitance to earth. Large voltage swings that can result in SWER supplies can cause serious damage to motors.

Protection of motors against brown-outs

As to motor damage, take the example of a motor driving a high inertia load. A large voltage drop might cause the motor control contactor to drop out. When voltage comes back after a brief sag, the rotor is still spinning and not necessarily much below synchronous speed. The combination of the rotor back-emf working against the supply voltage, the two no longer in phase, can cause a catastrophic motor failure, damaging its insulation beyond repair.

UPS system reliability

Mission-critical loads are usually supplied by UPS systems. The double conversion on-line UPS is generally used for ratings higher than 10 kVA. Although a sophisticated technology capable of delivering high power quality output voltage, it is subject to the effects of voltage regulation on the input. Large sags will bring on the battery bank but smaller voltage drops depending on their duration, may do the same, and therefore, almost surreptitiously, lower the amp-hour capacity of the battery bank.

Auxiliary generators, etc

Generator supplied loads, therefore including those backed up by an auxiliary generator, may well require a voltage regulator. The relatively high sub-transient reactance of generator windings are much affected by poor power factor. Therefore loads sharing circuits with heavy electrical gear such as large motors, may well need their own voltage regulator.

TSi Technology

The TSi technology is based on an IGBT converter-inverter operating on a in-line, buck-boost transformer. There are two powerstacks, one being the converter supplying DC to the inverter which provides correcting AC voltage to the buck-boost winding. A microprocessor circuit compares the output voltage against an internal reference, and alters the pulse width modulation to the inverter. The TSi VRP voltage regulators include surge protection on the input side and have noise reduction input and regulated output filters.

The TSi technology compare very favourably with servo voltage regulators (these typically have a response time of 200 milliseconds) and electronic tap changers, which have settling times of the order of 50 milliseconds. TSi VRP voltage regulators have a response time of 20 milliseconds.

Wide range of ratings

The TSi VRP voltage regulators cover ratings from 1 kW, single phase to 50 kW, three phase. Features include automatic bypass in the unlikely event of equipment failure, low insertion impedance, low weight per kW rating because of judicious selection of magnetic components, caster mounting and low emitted noise.

TSi VRP voltage regulators in brief
The TSi VRP precision voltage regulators are designed for indoor use and suit applications including mobile phone cells, microwave relaying stations, remote telemetry, etc. and a variety of other industrial and commercial as well as scientific duties. The VRP microprocessor-based voltage regulators employ IGBT-based 20 kHz PWM-converter-inverters and buck-boost transformer to provide very low distortion precision-regulated voltage with less than 3% variation as well as very fast response to step changes within 20 milliseconds. An automatic bypass provides assurance that in the unlikely event of equipment failure, voltage for mission critical applications is still being supplied. The VRp voltage regulators are designed to meet IEC60950 and to provide excellent surge protection. In addition a noise filter is provided for the regulated output.

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