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Best Applications and Case Studies

Built to last
Systems In The Field

T-Star personnel have customized, built, and installed more than 150 thyristor-switched SVCs worldwide since 1998. Our focus has been on the SVC solution alone, making us the premier specialists in the power correction field.


T-Star's SVC Systems are guaranteed to:

  • Meet or exceed utility- or end user-specified Operating Voltage Stability, both initially and after extended periods of operation

  • Demonstrate easy customer operation and maintenance

  • Experience high target levels of reliability

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Large Motors and SVCs

Starting motors require more energy

During starting, AC motors often draw 6 (or more) times electric current than the same motor operating at full load. Initially, the motor draws mostly reactive VArs, followed by a transition to drawing mostly real watts. 

The most common way to start motors is to draw the full amount of transient power from the AC power system.  If the motors are too large, the power flow will cause a drop in the power system voltage level, which often extends starting time or prevents the motor from starting altogether.  As a result, large motors often require the purchase of additional motor starting equipment.

Big Motor Starting Problems
Three Most Common Solutions

  • SVCs operate directly on the power system voltage by injecting VArs. The motor bus voltage can be controlled directly and dynamically, thus allowing the motor to be started at or near its full starting-torque level.

  • RVSSs limit the amount of current available to the motor through phase-angle control. An RVSS reduces the motor-starting current and the starting acceleration rate, thus the motor is started gradually to reduce the impact on the power system.

  • VFDs convert the 60 Hz AC power to DC, then back to AC at a variable frequency. The motor is initially "turned over" at low frequency. The frequency is gradually increased to bring the motor to full-speed.

Three Common Choices

A T-Star SVC System is a bus-level solution and can start multiple motors without modification. It's also harmonic-free.

  • An RVSS is a proven solution where reduced acceleration (reduced torque) during starting is acceptable (or desired). It is a harmonic-generator.

  • A VFD allows a motor to remain on its speed/torque curve. It is very often the most expensive solution, can be overkill in a motor-starting application, and generates harmonics.

Best Application
Starting Large Motors

Water System Case Study

North Texas Municipal Water District (NTMWD) supplies municipal water authorities all over Texas, using large lakes as water resources. One of the largest is Lake Texoma.


NTMWD's Lake Texoma station began with two 4,000 HP, 4160V pumps.  Due to increasing demand, NTMWD purchased an additional two 6,100 HP, 4160V pumps for the same station. They were specified, quoted, and installed with soft-starters. The soft-start system was unable to start the new motors. After analysis, it was discovered that the power system was not capable of supplying enough power to start the motors.


The solution was a 2-stage, 12.2 MVAr Dynamic VAr system configured by T-Star. It was built, shipped, and installed by T-Star.

Best Applications

Pump Station Case Study

Piedmont EMC, located in Hillsborough, North Carolina receives power delivery from an investor owned utility (IOU) via a radial 44 kV line. The 44 kV line serves two Piedmont EMC 44/12.47 kV substations before terminating at a 44/5 kV substation dedicated to a pipeline customer immediately adjacent to the substation.


  • Starting 1 or 2 motors created a 10%+ sag on a 44kV system that also served residential customers.
  • Residential customer complaints increased.
  • The initial choice was the installation of fast-switched capacitors, which resulted in problems typically associated with conventional capacitor-switching.


A custom built T-Star SVC system was purchased and installed on the distribution circuit. The sag issue was corrected.

System Location Study

Piedmont EMC needed to figure out where to physically locate the SVCs. Location was an integral part of the process. Their careful analysis led to a few important observations:

Observation 1

Placing the SVC on one or more 12.47 kV buses was studied. Simulations suggested that use of a single SVC system at the closest substation would yield results comparable with individual SVCs at each substation for about half the cost.

Observation 2

Placing the SVC directly on the 44 kV line was considered and discarded as being more expensive. Transformation would be required, and the total price of the SVC system could easily double.

Observation 3

Locating an SVC on the 5 kV bus provided the best isolation due to the impedance between the 5 kV station and the other two Piedmont EMC substations. However, Piedmont EMC had no other 5 kV substations, and a 5 kV SVC would not be reusable.

Location Diagram

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Piedmont EMC One-Line Diagram

Piedmont System Details

The SVC selected for this application was rated at 8.4 MVAR, 3-phase, and it provides 7 levels of capacitive support in increments of 1240 kVAR. This step-size equates to a 3.2% step voltage change at nominal voltage, and was chosen using IEEE 1453 and the GE Flicker Curve based on the frequency of the motor starts.

Subsequent field measurements revealed an effective SVC voltage resolution of less than 3% during motor starting. The figure shows the actual results of the starting of one of the pump motors with the SVC in-service.

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First Pump Motor Start with SVC In-Service


The SVC unit was installed in 2004. It has never missed a beat. In 2008 and 2016 the SVC control was upgraded and continues to perform reliably today.

Piedmont’s careful consideration of alternative SVC locations resulted in a system with substantial residual value. By taking the responsibility for the SVC’s pad and wiring, they minimized their costs and developed an initial familiarity with the SVC. Much of the routine SVC maintenance is performed by Piedmont EMC line crews.

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T-Star's Post Installation Involvement

Piedmont purchased our extended service plan. T-Star regularly accesses Piedmont's SVC data history and checks system performance. In the rare event of problems, we are able to diagnose to the component level for replacement. We gain access to the data remotely.

Best Applications
Bus Stability

Frequent and continuous motor loading and unloading occurs in many different industries.

Some processes use DC drives, others use AC motors. While the internal operating differences are significant, the power system effects are similar.

  • Each process results in significant regular changes in the mechanical power required to perform the intended work.
  • Mechanical power is ultimately converted from the electrical power source. Variations in electrical loading (from AC motors and inverters) distort and affect their mechanical power requirements.

The loading variations always cause corresponding voltage variations on the plant power bus.

Bus Stability and Our SVCs

A T-Star SVC System will:

  • Cancel VAr flow on the plant bus.  This cancellation significantly reduces power flow through cabling, switchgear, and transformers.

  • Reduce DC drive hunting due to voltage swings.

  • Maximize AC motor torque.

Bus Stability

Remote Mining Facility-REA Energy Case Study

REA Energy, a 5,000 member co-op headquartered in Indiana, Pennsylvania.


  • Multiple coal mines located on a single circuit
  • Customer flicker complaints


The two mining operations were located in the same area, approximately three miles apart.  Each used continuous miners to push several AC motor-powered cutting heads into coal seams to remove material. Profitability is proportional to output, and miners push the cutters as close to locked rotor as possible before withdrawing them from the coal-face to regain speed.

For flicker mitigation purposes, each site was modeled as a series of independent motor loads.  The large motors (powering cutter heads) were modeled as motor loads varying from idle to near locked rotor conditions.  The other motors (conveyors equipped with reduced voltage soft-starters) were modeled as randomly-varying loads going from no load to full load.  Steady state loads such as mine ventilation and pumping systems were ignored for flicker analysis, but were included for power flow, power factor, and harmonic analyses.

With one mine in-service, customer complaints began to increase.  A second mining company requested service, and both companies had indicated plans to increase load.  In addition, the REA had also received notice from a third mining operation that was planning to locate in the same area.  All the mine operations would be served from the same 12.47 kV circuit fed from a 46 kV substation.

Considering how to address the flicker, the REA was aware that typically these small mines in Appalachia last three to fifteen years.  Even if reconductoring the 12.47 kV line would yield acceptable flicker mitigation, it would also result in a permanent high ampacity upgrade to a circuit that would have a maximum use of only seven years.

Flicker Solution

Choosing an SVC, the REA was able to reduce its initial costs and still have a reusable asset when mining ceased. During the planning process, the REA discovered two additional concerns: whether each mine would require an SVC, and the effects of the addition of a third mine on the circuit.

Since the circuit is not dedicated to the mining customers only, other customers are affected by flicker from mining operations. Analysis of the line impedance between mines showed that locating the SVC immediately to the source side of the first mine, and then correcting to levels below the IEC flicker table (Table A. 1, IEEE-1453), would limit flicker at the respective mine entrances to acceptable levels. Thus, one SVC could be used to treat all mining loads.

The flicker caused by the first two mines was addressed by using a 7-step SVC rated at 2.4 MVAR. See the oneline diagram in the figure below.

The addition of the third mine would increase the maximum flicker levels and require a larger SVC than was required to serve two mines. If the third mine came on-line, resulting flicker problems could be solved by designing the SVC for an in-field expansion. SVC installations are designed for field expandability: In this case, the system can be expanded to a 15-step SVC with a rating up to 6 MVAR by the addition of three static valves and suitable capacitors.

Since the third mine has not yet started, this SVC design proved useful.  The REA did not invest in unneeded capacity.

In 2014, the two mines expanded.  T-Star, working with the customer, was able to:

  • Update to the next generation of controls

  • Add two 1200 kVAR vacuum-switched filter banks to provide base-load voltage support, thus extending the capacity of the existing SVC.
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REA Energy One-Line Diagram

Best Application
Bus Stability

A Refinery Case Study


  • Two 7,000 HP motors on one 12.47kV bus. 
  • Voltage sags during starts made starting unpredictable.
  • Utility sag was too high.


12 MVAR-rated T-Star SVC System, sized to reduce 12.47 kV motor-start voltage sag from 11% (uncorrected) to 3.5%.  The sag on the utility transmission system was reduced from 7% to less than 2%.

What did they get for their money?

Easy purchase process-T-Star built and installed the system.

Reliability-The SVC has been performing flawlessly since 2006.

Performance-Sag is reduced to acceptable levels.

Justifiable ROI-Refinery operational costs are lower.

Peace of Mind-We stand behind our products.

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Refinery Decision Making Process

The customer preferred this solution over a soft-starting system because a soft starter was unable to satisfy utility sag requirements. Also, a soft-starter would not reliably start the motor. A VFD was not considered for starting due to high cost and complexity. The refinery needed flawless and reliable performance. Process shut-downs were unacceptable.


Best Application
Arc Welding

Welding and Asymmetric Electric Loads Case Study


A manufacturer of computer flooring using 36 independent single phase welders was causing unacceptable voltage flicker on the serving utility's circuits.


A 6 MVAR-rated TSC, designed to reduce 13.2 kV voltage flicker from an uncorrected Pst of 3 to a corrected Pst of less than 1 at the point of common coupling (PCC).


  • The Modular TSC design provided a system that reliably meets the operating requirements. (A more expensive option, with Pst < 1.1 was also offered).

  • In service since 2007, this system has shown extremely high reliability, with an extended MTBF over the years.

  • Customer preferred this solution over obtaining a transmission level connection with the utility at a cost over $2 million. Unit is deemed “must run.” Customer cannot operate more than 1 shift without it.

  • When a newly-enhanced control system became available, customer elected to upgrade the controls in the field.

  • T-Star performs ongoing remote monitoring and assistance as requested.

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Active browser-based display showing 30 seconds of real-time operation on standard controller screen. The welding patterns do not repeat and each phase operates independently of the other 2 phases.

This chart is derived and shows how each of the 3 phases react differently in order to maintain a stable 3-phase voltage.

Based on this information it is not surprising that the unit operates nearly continuously on each of the three phases.

The high number of switching operations requires a rapid and accurate controller as well as a system that is able to switch billions of times without excessive wear and tear.

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An excerpt from a standard control system screen is shown here. Note that Valve C4 (Phase C) shows approximately 106 million operations - for 14 months of operation. 

This SVC system will experience billions of operations per valve. Properly maintained solid state devices don't experience wear and tear from daily operations.

Operational success is defined here as meeting agreed-upon performance standards for reliable operation.  Some of these standards include:

  • IEEE 1493—Flicker standard, largely adopted from the IEC flicker standard. Its scope includes the measurement and remediation of periodic voltage fluctuations. Measurements include: Voltage perturbations, Pst (short-term) and Plt (long term).  The GE Flicker curve is also cross-referenced for specific flicker patterns.

  • IEEE 519– Power Quality standard, primarily about harmonics, secondarily voltage fluctuations. Metric includes the GE Flicker curve.
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Measured Response Times:

NOTE:  Actual event response time varies based on the phase angle at the time current flow triggers a response.  The responses shown at above and at right approach the theoretical maximum response time for this event.

Measureable motor current flow begins as the Phase A window closes, almost 120° (0.33 cycle) before Phase B responds. Any earlier and Phase A would have responded later and phases B and C would have responded in less elapsed time.

Phase Response Order Time from Event (sec) Time from Event (cycles)
B 0.0053 0.318
C 0.0113 0.678
A 0.0165 0.99

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