Page 21 of 190 Report No.: 6068396.50 TRF No. G99/1-4_V1.0 G99/1 Clause Requirement - Test Result - Remark Verdict 9.5.1 Instability in Distribution Networks may result in unacceptable quality of supply and tripping of Generator’s plant. In severe cases, instability may cascade across the Distribution Network, resulting in widespread tripping and loss of demand and generation. There is also a risk of damage to plant. P 9.5.2 In general, System Stability is an important consideration in the design of Power Generating Module connections to the Distribution Network at 33 kV and above.
Stability considerations may also be appropriate for some Power Generating Module connections at lower voltages. The risks of instability generally increase as Power Generating Module capacity increases relative to the fault level infeed from the Distribution Network at the Connection Point. P 9.5.3 System Stability may be classified into several forms, according firstly to the main system variable in which instability can be observed, and secondly to the size of the system disturbance. In Distribution Networks, the forms of stability of interest are rotor angle stability and voltage stability.
P 9.5.3.1 Rotor angle stability refers to the ability of synchronous machines in an interconnected system to remain in Synchronism after the system is subjected to a disturbance. N/A 9.5.3.2 Voltage stability refers to the ability of a system to maintain acceptable voltages throughout the system after being subjected to a disturbance. P 9.5.3.3 Both rotor angle stability and voltage stability can be further classified according to the size of the disturbance.
N/A 9.5.3.4 Small-disturbance stability refers to the ability of a system to maintain stability after being subjected to small disturbances such as small changes in load, operating points of Power Generating Modules, transformer tap- changing or other normal switching events. P 9.5.3.5 Large-disturbance stability refers to the ability of a system to maintain stability after being subjected to large disturbances such as short-circuit faults or sudden loss of circuits or Power Generating Modules.
P 9.5.3.6 Traditionally, large-disturbance rotor angle stability (also referred to as transient stability) has been the form of stability predominantly of interest in Distribution Networks with synchronous machines. However, it should be noted that the other forms of stability may also be important and may require consideration in some cases. N/A 9.5.4 It is recommended that a Power Generating Module and its connection to the Distribution Network be designed to maintain stability of the Distribution Network for a defined range of initial operating conditions and a defined set of system disturbances. P