Ontario Hydro System Research Articles

APPLICATION OF INERTIAL LOAD TO A LOSS OF GENERATOR POSTMORTEM

ABSTRACT The inertial load flow technique [2] is applied to a dynamic equivalent [1] derived from a NERC (North American Electric Reliability Council) data base to compute maximum tie line power flows for a 1980 MW loss of generation at the Nanticoke station in the Ontario Hydro system. The results were compared with a transient stability simulation and recorded tie line power and frequency measurements. The inertial load flow results were more accurate in capturing the filtered measurements of power flows during the first three to five seconds after a loss of generation contingency than the transient stability simulation. The transient stability simulation was shown to contain both synchronizing oscillations between generators as well as the quasi steady-state behavior captured by the filtered power measurements and inertial load flow. The inertial load flow is an excellent tool for estimating proximity to voltage collapse since the field current limiters on exciters utilize filtered measurements of the inertial response that occurs 3-5 seconds after a loss of generation contingency. The loss of voltage control and reactive generation supply due to action of field current limiters is a principle cause of loss of voltage stability in power systems. The inertial response is shown to capture a filtered estimate of the peak of the deceleration wave that propagates from the point of disturbance and would indicate whether the filtered estimate of these peak real power flows would incur sufficient filtered generator field current levels to cause field current limiters to act. Generator field current levels rise in an attempt to counteract voltage decline and increase in reactive losses caused by the peak power flows that are observed in the inertial response. The action of the field current limiter reduces field current and reactive supply to prevent thermal damage to the generator. The action of field current limiters initiates the voltage decline that can result in voltage collapse.

Performance of distance relay mho elements on MOV-protected series-compensated transmission lines

It is shown that the applicability of memory-polarized distance relay mho elements to the protection of MOV (metal oxide varistor) protected series-compensated lines is dependent on the system configuration, line loading, the location of the potential source, and the magnitude of memory polarization. For a configuration with compensation at one end of a line, the results indicate certain advantages in using the potential from the line side of the capacitor, and the use of a relatively large magnitude of memory polarization. The presence of a conducting MOV enhances the performance of the mho element both in terms of security on reverse faults and dependability on forward faults. The results obtained pertain to the proposed application in the Ontario Hydro system of a relatively large amount of compensation at one terminal in each circuit of a double-circuit line.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An analytical technique to evaluate station one-line diagrams in a network context

A technique is presented for analyzing station one-line diagrams from the point of view of their impact on the entire power network. In order to quantitatively and systematically evaluate alternative station layouts, including their impact on the overall transmission network, and to ensure that all design and operating criteria are addressed, a computer program called the Stations/Network Analysis Package (SNAP) was developed. A description is provided of how the approach was used to evaluate the arrangement of two stations in the Ontario Hydro system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new generation scheduling program at Ontario Hydro

The new daily generation scheduling model for the Ontario Hydro system is presented. The model is capable of considering the thermal and hydraulic systems together with system reserve requirement and transmission losses. The hydraulic system is considered in a detailed formulation that can handle river couplings in a complete manner. Inability to do this was a major weakness in the peak shaving technique used since early 1970s. A special network programming technique has been used to solve the problem. This method has proved to be very efficient from a computational point of view. Test results from application of the new technique are presented and compared to the peak shaving method. The user has estimated 1.4 million dollars per year of savings from the new computer package. >

Transient stability analysis of stressed power systems using the energy function method

The authors outline the nature and characteristics of the transient response of a large stressed power network. Transient stability analysis of such a system by the transient energy function method requires overcoming a number of analytical and numerical problems. These issues are identified and solutions to them are proposed. The procedure developed is tested on two realistic power networks derived from a large power flow base case of the Ontario Hydro system. Results of the tests compare well with time simulation and accurately predict the complex dynamic behavior. >

Load Models for Large-Scale Stability Studies from End-User Consumption

This paper summarizes improvements in the application of load models in power system stability studies by utilizing end-user energy consumption data to identify the composition of loads. The project included derivation and compilation of customer load characteristics for the Ontario Hydro System and subsequent interfacing with a transient stability program. Results from these models were compared with recordings of a recent Ontario Hydro system disturbance.

Probabilistic Short-Circuit Uprating of Station Strain Bus System???Overview and Application

Increasing levels of fault currents in the Ontario Hydro system have made the designs of some existing 230 kV strain bus station installations inadequate if conventional deterministic design techniques are employed. Uprating costs could be reduced by several million dollars per station, if a greater short-circuit capability for the existing strain bus and structures could be established using new probabilistic techniques. For this purpose, a multi-discipline task force from a variety of divisions within Ontario Hydro was created to evaluate 230 kV insulator string failure probabilities at Middleport Transformer Station (TS) and assess the impact of possible failures in terms of personnel safety, repair costs, outage costs, and system reliability. This paper and the three companion papers present an overview of the probabilistic uprating process as applied at Middleport TS. The study indicated that only marginal work (if any) is required to maintain adequate safety, reliability and cost criteria, assuming that currents are limited to within the existing 230 kV circuit breaker ratings.

Assessment of Real-Time Optimal Voltage Control

This paper reports the results of a detailed study of on-line voltage/var control performed on the Ontario Hydro system. The first part of the study is an assessment of active transmission loss savings obtained by optimizing generator voltages and transformer taps with an Optimal Power Flow program using data from a state estimator. In the second part of the study, the question is addressed of how frequently the generator voltages and transformer tape should be optimized in order to achieve a large percentage of the loss savings indentified in the first part. The study showed that the reduction in active losses is sufficient to justify further effort toward implementing voltage control. The results of the second part showed that for the load curve studied, most of the savings could be achieved with voltage control cycle times of about one hour. A new quadratic programming-based optimal power flow algorithm is also presented which exhibits execution times suitable for real-time applications. Sample execution times are given for various systems which confirm that exact optimal power flow solutions can be obtained in a fraction of the control cycle times suggested in the second part of the study.

Probabilistic Short-Circuit Uprating of Station Strain Bus System-Overview and Application

Increasing levels of fault currents in the Ontario Hydro system have made the designs of some existing 230 kV strain bus station installations inadequate if conventional deterministic design techniques are employed. Uprating costs could be reduced by several million dollars per station, if a greater short-circuit capability for the existing strain bus and structures could be established using new probabilistic techniques. For this purpose, a multi-discipline task force from a variety of divisions within Ontario Hydro was created to evaluate 230 kV insulator string failure probabilities at Middleport Transformer Station (TS) and assess the impact of possible failures in terms of personnel safety, repair costs, outage costs, and system reliability. This paper and the three companion papers present an overview of the probabilistic uprating process as applied at Middleport TS. The study indicated that only marginal work (if any) is required to maintain adequate safety, reliability and cost criteria, assuming that currents are limited to within the existing 230 kV circuit breaker ratings.

Dynamic Security Assessment Utilizing the Transient Energy Function Method

This paper presents applications of an efficient computerized technique for power system dynamic system security assessment using the transient energy function (TEF) method. The technique exploits the sensitivities of the unnormalized transient energy margin with respect to operating indices and critical interface flows in order to arrive at the stability limits for various system outage states and operating conditions, that would be required for on-line application. The paper describes the sensitivity technique and demonstrates a practical application to the dynamic security problem in one portion of the Ontario Hydro system including results of the validation and accuracy tests of the technique.

Risk Assessment of Grounding Hazards due to Step and Touch Potentials Near Transmission Line Structures

Excessive step and touch potentials near high voltage transmission line structures due to severe ground faults present a hazard to anyone in proximity to a structure when a fault occurs. This paper extends the probabilistic analysis of step and touch potentials near transmission line structures reported at the 1982 IEEE Summer Power Meeting [1] and presents a complete computerized methodology for assessing the overall effectiveness of grounding for any given network and right-of-way conditions. The paper also illustrates some applications of the method in the Ontario Hydro system.

Cement Growth Failure of Porcelain Suspension Insulators

The paper provides the results and analyses oFinvestigations into porcelain suspension insulator failures on the Ontario Hydro system. The high failure rate of suspension insulators on transmission and distribution lines has been attributed to the volume expansion of the neat cement, a process commonly referred to as growth. Analytical analysis of the suspension insulator design and autoclave expansion tests on insulators support the cement growth failure mechanism.

Characteristics and maneuverability of CANDU nuclear power stations operated for base-load and load-following generation

The characteristics and maneuverability of pressurized heavy water nuclear power units operated for base-load and load-following generation are discussed with respect to the requirements of Ontario Hydro. The nuclear generating units of Pickering G.S. 'A' (Units 1-4) and Pickering G.S. 'B' (being designed for Units 5-8), and the turbine-generator-grid of Bruce G .S. 'A' (Units 1-4) were simulated on digital computers. Simulation tests such as normal loading and unloading at various rates, grid frequency upset, and grid islanded cases were conducted with the unit load regulated by three alternative unit power control systems. The results of the simulation show that the necessary flexibility in power maneuvers to meet the load-following requirements in the Ontario Hydro system may be obtained with the CANDU-PHW (Canadian Deuterium Uranium - Pressurized Heavy Water) generating units controlled by an integrated unit load control system which normally operates in a reactor-following-turbine unit control mode. The simulation results also show that the reactor-following-turbine unit control improves the control of many process systems and the overall plant performance.

Transient Recovery Voltages on Power Systems Part I - Analysis and Tests of the Ontario Hydro System

Transient Recovery Voltages on Power Systems Part I - Analysis and Tests of the Ontario Hydro System