System Continuous Operation

The steady state parameters in the real-time monitoring software determine the system components loading, over/under voltage situation, frequency drop, active and reactive power flow, losses and so on. The main generator control VI also presents the generator’s loadings in order to share the generation level optimally when one of them encounters an overload situation. The constant active power-voltage magnitude generators known as PV generators, G2, G3 and G4, should participate in generation according to the control commands after the system start-up. Hence, their active power is increased to a reasonable value according to the system total load and the slack generator loading. This procedure was implemented manually by entering a proper torque command to the prime mover as shown in figure 5.11. The system’s active power load is increased in steps of 300 W for each load in different times (L1, L2, L3 and L4). Without any change in generation, the slack generator is responsible to maintain the system frequency at 60 Hz. Therefore, the total load change leads to an increase in the active power generation of the slack generator, G1. Increasing the active power of the generators will alleviate the total generation of G1. The active and reactive power changes of all four generators are shown in figure 5.11. Practically, the reactive powers return back to their initial values since the total reactive load was constant during the experiment.

A real-time power controller was implemented to monitor the active power of the load buses and specify the same amount of power to the nearest generator. This is the automatic power sharing process in order to show the effectiveness of the integrated real- time monitoring and control in wide area system. Figure 5.12 shows the active and

119

reactive power change of every generator which was controlled automatically by the real- time software. Similar to previous experiments, the same increase in load pattern was considered in this case and test results of this controller were compared with the manual generation control. Whenever a load is increased, the monitoring and control system recognized it. The system also changes the torque control command of the generator connected close to that load to change the amount of generated power. This procedure is clear as presented in figure 5.12. Since the monitoring system has a time latency of about 1 sec, the control system will follow the load variation by a step change within a same or twice time delay. The automatic control scheme is fast enough to operate the system in a smart manner and to share the load among the generation stations. The range of variation of the active and reactive power of each generator in the automatic mode is less than manual control because of the fast response of the control system. Figure 5.13 shows the benefits of automatic generation control system versus manual control through the voltage and frequency changes for the slack generator.

The automatic control system for the generators should be comprehensive considering system conditions such as loadings of equipments, voltage and generation limitations as well as stability issues. The use of the real-time software makes it possible to monitor all system conditions and create a proper power sharing algorithm such as Optimal Power Flow (OPF). Figure 5.14 shows the developed integrated wide-area system on the laboratory-scale Smart Grid test-bed with including monitoring, control and protection systems with fast communication features. The implementation of this system in the real-time software creates an environment for studying and verifying new control and protection schemes for the whole power system.

120

Figure 5.11: (a) Active power and (b) Reactive power of generators during load increase in manual control

Figure 5.12: (a) Active power and (b) Reactive power of generators during load increase in automatic control

(a) (b) (a) (b)

121

Figure 5.13: (a) Voltage and (b) frequency of generators during load increase in manual (upper plot) and automatic (lower plot) control mode

This system was used for studying integrated wide area control and protection system to monitor the system status for abnormalities such as over/under voltage, overloads of equipments and any other conditions. This system was also used to monitor real-time system stability and security margin. The indices formulation and their implementation on wide area monitoring and control centers were presented. This provides an applicable view of system stability and security margin using PMUs in wide area networks. The voltage stability indices were measured during the operation of the power system when the load changes take places. A wide area monitoring system with high data resolution rate was developed. This system was designed to have capabilities such as maintaining system normal operation and take a proper remedial action when encountered by unexpected circumstances by monitoring critical states in wide area system. As a result, the system operator will have proper knowledge and visualization about the power system's current situation and the distance of stability margin.

122

Figure 5.14: Overall implemented real-time system for integrated wide area monitoring, control and protection systems Start

Read Real-time CTs & PTs data from DAQs

Voltage Amplitude & Phase Current Amplitude & Phase Voltage Sequences Current Sequences Active & Reactive Powers Network Impedance Frequency Unbalance Factors

Switch Control & Topology Change Set Slack Generator @ fn Manual Load level Control Set next generator in Torque Control Mode Automatic Dynamic Break Controller Safe to Synchronize Connect Generator and set the torque All System Connected System Startup Control Manual Power Sharing Automatic Power Sharing Display: Voltage Phasors Current Phasors Power Curves Loadings System Topology Transmission Line Parameters Calculation Display: Transmission Line Parameters Voltage Stability Indices Display: Voltage Stability Indices and margins Wide Area Monitoring and Awareness System

Over/Under Voltage

Rate of Change of Voltage (ROCOV) Over/Under Frequency

Rate of Change of Frequency (ROCOF)

Time Over-current MHO Distance Relay Polygonal Distance Relay Inverse Power Flow Voltage Unbalance Function Current Unbalance Function

System is Safe Trip Decision Intelligent Protection System System Topology Wide Area Protection System

Phase Difference @ different buses Wide Area Control

Generators Torque

Power-torque look up table

Data Transfer via Engine Mode Power Factory Analysis Package N-1 Contingency Analysis Result Optimal Power Flow System Analysis H igh Speed d at a Yes No Yes No No

123