Voltage Security in Philippine Power Systems

Voltage security in power system planning and operations is an important factor of grid and distribution codes in the Philippines. The power system, system components and customer devices respond to the magnitude of voltage in a manner that would impact its operation. Power system interruption cascades when voltage collapse is experienced. Generators and other system elements tend to be saturated when keeping the voltage secured at certain limits. Customer devices might misoperate or may expel from its connection point when voltage is not appropriately within the devices’ operating regions. These are some of the reasons why it is important for a power system to be planned and operated in terms of voltage security. With areas where generation deficit is a problem, voltage security is hard to achieve since generators provide and assist in keeping the voltage secured in terms of reactive power management.

Philippine transmission systems must be operated in normal conditions within voltages of 0.95 per-unit up to 1.05 per-unit while distribution systems are expected to have voltage levels from 0.90 per-unit to 1.10 per-unit. These voltage magnitudes should be kept in steady-state conditions. Scheduled maintenance of lines and other components must be conducted making sure that these voltage performance standards must be kept. When a fault or a transient event occurs, the voltage levels can not deviate from 0.90 per-unit to 1.10 per-unit as long as 0.00833 seconds to 60 seconds. In this case, voltages magnitudes are classified as voltage sags or swells. Above 60 seconds, and the voltage levels are still deviating from the said limitations, these voltages are called long duration voltage variations.

Voltage security can be planned and operated by reactive power management and predicting the voltage profile in contingency analysis. Reactive power supervision entails updated reactive power capability curves of existing generators and list of static and dynamic reactive power devices installed in the power systems. When running a post-contingency voltage assessment, the reactive power capabilities of generators, reactors, capacitors and static VAR devices (SVDs), and operating points of tap-changing transformers, must be considered since these options can be enable in running appropriate post-contingency power flow solution. The area/zone/buses in study must be identified by the power system engineer(s) for proper scenario and conditions setting. The voltage ranges limits and voltage deviation limits must be defined for the area or zone or buses in study for analysis purposes. Together with the identification of the area in study, possible system contingency scenarios, assigning of voltage limits at the area in study the power flow solution or transient simulation can be automatically configured to report all the violations as a result of each probable contingency. Usually, in power flow computations, these can be presented in tables or graphs while for transient simulations, whether in phase domain or time domain, these voltages are analyzed using time versus voltage plots.

Philippine power systems just like any other power systems must be operated in voltage security. Voltage must be operated and planned accordingly for the power system and its components to operate securely. Codes define limitations and thus appropriate prediction and prevention of unsecured voltage can be analyzed. Knowledge of existing reactive power devices in the power system and proper coordination of these devices will enhance voltage security together with applying computer solutions that can automatically provide flexible programming of studying areas of voltage violations.