Latency Viewed as a Stochastic Process and its Impact on Wide Area Power System Control Signals

A method of calculating the communication delay (latency) for measurements and control signals in a power system is shown. The basis of the calculation is a dedicated communication channel for control signals. The time delay calculation is examined using a dynamic equivalent of the Western Electricity Coordinating Council transmission system. The impact on control system response is discussed. The application given is a wide area control system for interarea mode damping. Results demonstrate that control signal latency can degrade the performance of controls in a wide area control system.

I. Introduction

In modern power systems, there are a large variety of measurements that are communicated for purposes of control. Presently, the measurement and communications network in a power system is referred to as a wide area measurement system (WAMS) [1], [2]. with increased speeds of communications equipment and the introduction of a cadre of new measurement devices (e.g., phasor measurement units) in power systems, some power engineers have proposed that the existing WAMS can be used to implement wide area controls [3], [4]. The wide area control system (WACS) can be used to control a variety of components in a power system such as power system stabilizers, HVDC systems, and supplementary controllers for flexible ac transmission system (FACTS) devices. in a WACS, the time required to transmit data from the measurement location to a control center or data concentrator, and the time required ultimately to communicate these data to control devices, is collectively denoted as communications delay or latency. It is imperative that latency should be considered in the design phase.