Applying protection principles for controlling distributed generation
In a distribution system, it is essential to maintain the voltage variation within a specified limit for satisfactory operation of connected customers’ equipment. Normally, this goal is achieved by controlling the operation of compensating devices, such as load tap changing transformers, shunt capacitors, series capacitors, shunt reactors and static VAr compensators. However, technical and regulatory developments are encouraging a greater number of small generator units, known as distributed generation (DG), and this has the potential to significantly affect voltage control systems. This paper presents an adaptive voltage control technique that incorporates DG systems into the voltage control system. The control scheme uses on-load tap changing transformer (OLTC) and DG for voltage corrections, both are driven by advanced line drop compensators (LDC). At the substation, the LDC is employed to control step-up or step-down decisions of the OLTC, while another LDC will be used at the DG connection point to set DG parameters. Also, for a more cost-effective system, voltage control action coordination is proposed using magnitude and time grading. The control approach is tested on a modified distribution system with load variations that are stochastic in time and location. The results show that the integration of these magnitude and time grading protection principles have considerably reduced the DG energy required to achieve the desired control.