Prof. Alexander M. Bryantsev, Moscow Power Institute, Smolensk; Mark D. Galperin, PhD, Expanding Edge LLC, San Francisco; Prof. George A. Evdokunin, St. Petersburg State Technical University, St. Petersburg, Andrei G. Dolgopolov, Sc.D, All-Russia Electrical Engineering Institute, Moscow
Magnetically controlled reactors (MCRs) and thyristor-controlled reactors (TCRs) achieve similar benefits, but MCRs achieve them more reliably, more sustainably, without the usual "sudden death failure period" of TCRsó and at lower cost. Letís look first at some of the advantages of controllable reactors:
Transmission of higher power by existing power lines, due to increased steady-state power stability limits.
Smooth, automatic power regulation, minimized power loss, and significantly decreased switching operations, and hence less wear on switching equipment and transformer load tap changers.
Power savings of about 1 to 2% of transmitted poweró due to decreased grid reactive current and associated ohm loss by compensation of excessive capacitance with reactor inductance.
Without MCRs, currently installed capacitor banks control grid reactive load and voltage step-wise by on-off switching, and stepwise control is never ideally adequate to the actual state of the system.
MCRs achieve these benefits because they offer the advantages of much greater reliability, simplicity of maintenance, economy, and energy efficiency to power quality control. Here are some details.
Both TCRs and transmission-application STATCOMs use gate turn-off thyristors (GTOs) in their control systems, and both have initial 6-month "sudden death failure periods" (SDFPs) because these GTOs are likely to burn out as much as a couple of times per month when first installed. Unlike TCRs, and even unlike the newer STATCOMs, MCRs do not have this initial SDFP.
With their simple, transformer-like steel core, MCRs have transformer-like reliability, and are more reliable than TCRs or STATCOMs as FACTS controllers.
TCR or STATCOM systems usually contain hundreds of GTOs in their control systems, and one GTO failure in the control system per year for every 100 Mvar of reactive power is considered to be the best achievable rate of failure after an initial SDFP. MCRs have small and relatively inexpensive thyristor control systems, which operate at a low ~1% of the MCR's rated reactive power. Thus MCRs can easily be somewhat overbuilt and hot-tested at the factory to specifications higher than necessary, to ensure proper function after installation.
Also, because of the small size and low rated power and voltage of the MCR control system, spare control systems may be installed, if needed, as hot reserves.
MCRs last longer than TCRs. No MCR has been replaced in more than 20 years of field experience. There are currently more than 140 units in operation. The fact that production has tripled in the past 3 years shows the confidence that utilities have in them after many years of field experience.
The overvoltage limitation for MCRs is 2.3 times rated voltage, vs. 1.8 times for TCRs.
MCRs have a transformer-like, "plug-and-play" installation.
MCRs are as simple to operate and maintain as ordinary transformers are.
MCRs are as reliable as transformers.
MCRs cost twice less then TCRs of the same rated parameters.
MCRs require an installation space of about 10 sq. ft per Mvar, vs. 100 sq. ft per Mvar for TCRs with air-core reactors.
Without filters, the current-distortion coefficient of MCRs is about 3%, as against 5.8% for TCRs. Thus fewer filters are required.
At rated reactive power consumption, internal power losses in reactors of greater than 35kV rated voltage are only 0.4% in 180 Mvar MCRs and 0.7% in 32 Mvar MCRs. In TCRs of the same rated voltage, internal power losses are about 1.1% because TCRs of more than 35kV rated voltage require step-down transformers, which waste additional energy. MCR standby-mode losses are also lower.
Typical long-distance transmission results in power losses of about 3%. Controllable reactors reduce transmission losses by about 1/3, depending on network configuration.
In the context of Californiaís 50 GW consumption patterns, use of controllable reactors would effectively add a power plant of about 1/2 GW to the systemó without fuel cost, without ecological damage, and without negative political impact.
MCRs are the most economically advantageous way of gaining the benefits of controllable reactors for Californiaís system.
Please address correspondence to Dr. Mark Galperin:
Mark D. Galperin, PhD, General Manager
Expanding Edge llc 508 San Anselmo Avenue, Suite 1B
San Anselmo, California 94960 USA
Tel (415) 256-2512
Fax (415) 256-9268