Method for prevention of voltage collapse in power system. RU patent 2508590.

FIELD: electricity.

SUBSTANCE: method consists in measurement of voltage, active and reactive power on buses of the station, control of available alarms from a stationary automatics of the generator "imitation of current overload of a rotor" and if they are available from all generators connected to buses of the station, then trip of load of the controlled power district is performed with accurate determination of unloading volume, which is calculated as per the following formula: $$\Delta P_1=\frac{B-\sqrt{B^2-AC}}{A},$$ where A, B, C - design factors determined based on measurement of values of active power, reactive power and voltage on buses of the station.

EFFECT: elimination of a deficit of reactive power in the power district and prevention of avalanching voltage reduction.

The technical field

The invention relates to the electrical engineering, in particular to the means of emergency control of the power system, and is designed to prevent a cascading emergencies associated with the exponential decrease of the voltage.

The level of technology

The presence of scarce power districts and major transit power flows create the conditions under which in the event of disaster perturbations in the energy system to cover the deficit of reactive power operation of automatic excitation regulators (ARV) generators in power plants energy district and provision of reactive power is not enough. With the exhaustion of the reserve for reactive power generators are overloaded rotor current [1] and, as a consequence, either disconnected from the network effect of technological protections, or the voltage of the generator is not supported devices ARV within the specified limits. The process is associated with the lowering of tension in the area of the load is fed from power plants, probably as a result of the emergence of the process of voltage collapse of redemption consumers energy district.

The process of development of a voltage collapse can occur very quickly. Modern devices of automatics not always allow time to prevent an avalanche process, operate with a certain time delay.

There is a method of shutdown of the load in an accident in the power system, is used in automation undervoltage limitation (). Action of automatics is aimed at ensuring an adequate supply voltage at nodes load in the post-emergency mode emergency switching-off of the network elements [1]. Application allows to raise reliability of power supply of the remaining part of consumers and reduce emergency damage. Use is based on a preliminary calculation of a series of emergency situations in the power grid, as a result of calculation is determined by the location and volume control actions . As a controlled parameter voltage at nodes of the load. As a result of voltage reduction below set point produces off of the load. The execution of the action the stairs are different exposure time. Action with a total exposure time may not be sufficient to prevent voltage collapse.

Known way to maintain the required level of voltage in the power district with the help boost generators excitation [2]. The voltage drop in the load area ARV of each generator of this energy district, maintaining a given level of tension, increases rotor current and issuance of reactive power. With the exhaustion of the reserve for reactive power of overloading the power generators energy district rotor current with the action of the standard automation generator, which is part of ARV (limit congestion - OP), the reduction of the rotor current generators, which may lead to a further reduction of voltage in units of energy district.

Known also, a method of automatic unloading of generators of the plant for the static overload of transmission (arsp), described in [3]. In the specified way to control the loading of transmission (stations) is an active power. Automation fixes a situation when the real power for a controlled cross-section reaches a given threshold value and according to the given algorithm (with time delay or without it) acts on the unloading of transmission.

Causes of overloading transmission can be:

- the emergence of a sudden deficit of generating capacities in the admissions regarding the transmission part of the energy system caused by the disconnection of the generator (power unit), partial or total discharge of the electrical load of the power plant, Department of excess energy system;

- the emergence of a sudden excess generating power in transmitting regarding the transmission part of the energy system caused by Department of scarce energy system, reset the consumers of electric power due to close short circuit or operational reasons, put part of the load from the SCO;

- slow (the rate of change of the regime in power system) increase the flow of active power and phase angles for power transmission due to the lack of power reserves at power plants in the receiving part, or lack of adjustment of the range in the direction of discharge power plants on the transmit side, as well as due to error Supervisory staff;

- disabling the shunting of communication and as a consequence - situ controlled by a power line and increase of the angle.

Most often arsp is used to preserve stability under perturbations of the first two types. The maximum volume of discharge, carried out automatically in this case is

where R NB - estimated value imbalance, P .Σ - maximum allowable value active power flow in the test section, P 8%Σ - the value of flow in the test section, corresponding to 8%stock of the static stability, k f - frequency coefficient characterizing the share of power generator, the controlled section.

A P value of NB is taken equal to the most acute shortage of power in the receiving part of (or excess of power in transmission) when disconnecting the most powerful generator or power unit, Department of surplus (deficit) power districts.

The essence of the invention

From the analysis of emergency conditions it follows that the cause of voltage collapse is a deficiency of reactive power in the area of the load, which may later develop quickly and lead to an avalanche of tension and destabilization of the power system.

The aim of the invention is to create an effective algorithm for liquidation of emergency regimes that could lead to an avalanche-like low voltage and violation of stable operation of power system.

This goal is achieved by the fact that the load-controlled energy district is carried out with a precise definition of the volume discharge (disable)necessary to eliminate the overload generators rotor current.

For this measure voltage, active and reactive power station buses, monitor the presence of alarms from the standard automation generator «overcurrent limiting rotor» and the data are available alarms from all generators connected to buses station, perform load.

The required amount of discharge to eliminate overload rotor current and input mode in scope (DP 1 ) can be defined as follows.

Not to overload the generator rotor current is equivalent to the condition

E q ≤E q ,

E q - existing value EMF one generator or equivalent EMF generators station, E q - valid value EMF by the condition of the load current rotor defined on the basis of the normative characteristics of equipment.

The expression E q generator can be represented as:

where P, Q, U - values of active, reactive power and the voltage on the tire station - corresponds to the generator (station) at an emergency overload,

P 1 - the magnitude of the discharge, at which the rotor of the generator is reduced to an acceptable value, which is equivalent to the condition E q =E q ,

k - the ratio between reactive and active components of the generator power stations (tgφ),

X d - synchronous reactance generator or equivalent resistance of generators of the whole station along the longitudinal axis [Ohm].

Expression (1) appropriate written in the following form

where S is the full power of the generator,

x do.e. - synchronous reactance generator or equivalent resistance of generators of the whole station along the longitudinal axis in relative units.

(2) the quadratic equation relative values of P 1

Proceeding from this amount the necessary discharge energy district for the removal of the generator overcurrent rotor is defined as:

The amount of discharge is determined on the basis of the parameters P, Q, U tire station received in the course of the change of regime.

Timed shutdown of the calculated amount of load on the fact of abuse rotor current valid value will avoid disconnection generator equipment and cascading development of voltage collapse.

Realization of the invention

1. Nevel .., Ten EA Requirements for power transmission, which links the load node with the system (for the maximum capacity of the remote site load). - News NIIPT №64, 2010.

2. Ovcharenko NI Automatics of electric power stations and electric power systems. Textbook for universities./ amended ... - M: NC , 2000. - 504 C. [.410-414].

3. Gurevich J.E., .., Okinawan A.A. Calculations of stability and emergency control in power systems. - M: Energoatomizdat, 1990. - 390 S. [.233].

A way to prevent a collapse of voltage in the power network which consists that measure voltage, active and reactive power station buses, monitor the presence of alarms from the standard automation generator «overcurrent limiting rotor» and the data are available alarms from all generators connected to buses station, perform load-controlled energy district with a precise definition of the volume of unloading necessary to eliminate the overload of the rotor, which is defined as

where A=1+k 2 ,

the estimated coefficients, calculated on the basis of the measurement of the active R, reactive Q power and the voltage U tire station mode in case of emergency overload, S - full power generator,

x do.e. - synchronous reactance generator or equivalent resistance of generators of the whole station along the longitudinal axis in relative units, k - is the ratio between reactive and active components of the generator power stations (tgφ), E q - valid value EMF by the condition of the load current rotor defined on the basis of the normative characteristics of equipment.