Electricity: power supply or regulation systems – Including a transformer or an inductor – Polyphase or plural transformers
Patent
1997-03-24
1999-05-25
Wong, Peter S.
Electricity: power supply or regulation systems
Including a transformer or an inductor
Polyphase or plural transformers
323205, 307 87, H01F 3012, G05F 170, H02J 100
Patent
active
059072393
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method of enhancing capacity of transformer equipment for a polyphase AC network without augmentation of its short-circuit level, and an apparatus thereof. The invention also relates to a method of power flow control between two synchronous polyphase AC network busses, and an interconnecting apparatus therefor.
Although the methods and apparatus are directed toward different purposes, they are implemented with equipment having the following characteristics in common: synchronous polyphase AC transmission networks; different values, are subjected to phase-shifted voltages; then sufficient to add, in parallel with the existing branch, at least one branch constructed as described hereinafter; transformer or not.
1. Description of Related Art
The conventional technique for limiting fault currents in a transformer station consists typically to insert an inductance in series with a cable. However, such an addition of an inductance in series with the cable reduces the transmission capacity of the transformers in the transformer station.
Presently, if a transformer station becomes overloaded and it is impossible to install a transformer in parallel with the existing transformer(s) without for example overloading the network breakers located downstream of the transformer station during faults, the network owner can add a conventional transformer and divide the transformer station and its loads in two groups. The operating flexibility and reliability of the station are however reduced. Alternatively, the network owner can add a conventional transformer and replace all the breakers that can possibly be subjected to overloads during faults. The operating flexibility and reliability are preserved but at a cost that can become prohibitive if a high number of breakers must be changed.
Also known in the art are IPCs (Interphase Power Controllers), which are not designed nor intended for the purpose of enhancing the capacity of a transformer station. IPCs are rather used to force and/or regulate/control a power flow between two busses of a synchronous AC network while ensuring a limitation of the fault currents. IPCs involve the use of at least two reactive elements (a capacitor and an inductor) per phase, the reactive elements being external to and in series with the (phase-shifting) transformer used if necessary. The reactive elements are subjected to separately phase-shifted voltages.
Considering the steady state of transmission lines, improper power flows can depend on their lengths which are too long. In such a situation, series compensation may provide a way to reduce the line impedance and increase the power flow. However, it happens sometimes that the phase angle .delta. is simply too small to obtain a proper power flow even with series compensation. In such a case, a phase-shifting transformer can be used to obtain a power flow.
Known in the art, there is the document IEEE TRANSACTIONS ON POWER DELIVERY, vol. 8, no. 3, Jul. 1, 1993, pages 1420-1429, XP000403138 NOROOZIAN M. Et al. "POWER FLOW CONTROL BY USE OF CONTROLLABLE SERIES COMPONENTS" which describes a mathematical model for solving power flow control problems and providing information used to construct regions of feasible power flows of control lines. The model is devised for a line compensated by a series capacitor or phase shifter (i.e. a capacitor or a phase-shifter in series with the line). A mathematical formulation of the two fundamental series power flow controllers (controllable series compensation and phase-shifting transformer) have been developed in order to be compatible with load flow calculation programs. To illustrate the approach, a simplified network consisting of two parallel lines and of one power flow controller in series with one of the two lines is used.
Then, a general network model is presented to show that the new modelization allows the simultaneous use of many power flow controllers.
Also known in the art, there is the document YOUSSEF R. D. "PHASE-SHIFTING TRANSFORMERS IN LOAD F
REFERENCES:
patent: 4621198 (1986-11-01), Roberge et al.
patent: 5343139 (1994-08-01), Guygyi et al.
patent: 5517422 (1996-05-01), Ilic et al.
Historical Transformer Designs For Phase-Angle Regulating Equipment, by Stan Lindgren, published in FACTS, Apr. 1992, "Current Activity In Flexible AC Transmission Systems," pp. 67-69.
Noroozian et al., "Power Flow Control By Use of Controllable Series Components", IEEE Transactions on Power Delivery, vol. 8(3):1420-1429, (1993).
Youssef, "Phase-shifting Transformers in Load Flow And Short-Circuit Analysis: Modelling And Control" IEE Proceedings13 C, 140(4):331-336, (1993).
Bladow et al., "Experiences With Parallel EHV Phase Shifting Transformers", IEEE Transactions on Power Delivery, vol. 6(3):1096-1090, (1991).
Beauregard Fran.cedilla.ois
Brochu Jacques
Morin Gaston
Pelletier Pierre
CITEQ
Patel Rajnikant B.
Wong Peter S.
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