Ferry A. Viawan

Voltage and Reactive Power Control in Systems With Synchronous Machine-Based Distributed Generation

This paper investigates voltage and reactive power control in distribution systems and how the presence of synchronous machine-based distributed generation (DG) affects the control. A proper coordination among the onload tap changer (OLTC), substation switched capacitors and feeder-switched capacitors in order to obtain optimum voltage and reactive power control is proposed. It is assumed that there is no communication link between the OLTC and the capacitors, a normal case in distribution system operation these days. The results indicate that the proposed method decreases the number of OLTC operations, losses, and voltage fluctuations in distribution systems, with and without DG present. The power-flow reversal due to the DG is shown not to interfere with the effectiveness of the OLTC operation. Further, it is also shown that as long as the available capacitors are enough to compensate the reactive power demand, the DG operation mode does not give a significant effect to the distribution system losses. However, DG operating at a constant voltage is beneficial for a significant reduction of OLTC operation and voltage fluctuation in the distribution system.

Combined Local and Remote Voltage and Reactive Power Control in the Presence of Induction Machine Distributed Generation

This paper first investigates a local voltage and reactive power control (local control) in a distribution system based on local control of on-load tap-changer (OLTC), substation capacitors, and feeder capacitors, and how the presence of induction machine based distributed generation (DG) affects it. A proper coordination among those available voltage and reactive power control equipment to minimize losses in the distribution system, with and without DG, is formulated. Secondly, a combined local and remote voltage and reactive power control (local-remote control), which is based on automated remote adjustment to the local control in order to minimize the losses even more, is proposed. The automated remote adjustment in the local-remote control is also intended to keep the operating constraints fulfilled all the time, which cannot be achieved by using the local control when DG is present in the system. The OLTC and substation capacitors are assumed to be remotely controllable, while the feeder capacitors are not. DG with both constant power and varying power are investigated.

Coordinated voltage and reactive power control in the presence of distributed generation

This paper presents voltage and reactive power control methods in distribution systems in the presence of distributed generation (DG). Both uncoordinated and coordinated voltage control, without and with DG involved in the voltage control, are investigated. The uncoordinated voltage control means that all voltage and reactive power control equipment operate locally. The coordinated voltage control means that, in addition to the local operation, the voltage and reactive power control equipment will be adjusted remotely, based on wide area coordination, in order to obtain an optimum voltage profile and reactive power flow for a one-day-ahead load forecast and DG output planning. The result indicates that involving DG in the voltage control will result in a reduction of the losses, the number of OLTC operations and the reduction of the voltage fluctuation in the distribution system. Further, the results also indicate that the coordinated voltage and reactive power control, the losses can be decreased more.

Protection Scheme for Meshed Distribution Systems with High Penetration of Distributed Generation

This paper identifies the impact of high DG penetration on protection coordination and proposes a protection scheme to mitigate the identified problems, in a network with high penetration of DG. The scheme emphasizes on keeping most DGs on line to supply loads during the fault, without putting DG or any part of the distribution network in islanding operation, whilst ensuring that the conventional overcurrent protection devices (breakers with overcurrent relays - reclosers - fuses) do not lose their functions and their proper coordination

Probabilistic Approach to the Design of Photovoltaic Distributed Generation in Low Voltage Feeder

This paper presents the probabilistic approach to the design of photovoltaic (PV) distributed generation (DG) and its impact on low voltage (LV) feeder. Monte Carlo simulation is used to predict solar radiation and load, and an exact method is used to solve the power flow. The method is tested on two study cases, and the results are compared with those from deterministic approach based on commonly used scenarios. The probabilistic approach is shown necessary to obtain the optimum PV rating based on technical constraints and different objectives, including accepting a reasonable risk when needed. The results also indicate that PV-DG in a realistic case will most probably improve the voltage profile and decrease the losses on LV feeders

Voltage control with distributed generation and its impact on losses in LV distribution systems

This paper investigates the effect of DG, with and without reactive power control, on power losses in LV distribution feeders. The effect of load and feeder parameters, DG location and power factor is considered. A calculation method is presented and explained in detail, which proves to give accurate results as compared with one commercial load flow program. Moreover, simplified expressions are derived, which can be used to calculate the most appropriate size of DG unit during planning and/or to select the most appropriate mode of operation (active power generated) for an existing DG unit.

Voltage and Reactive Power Control in Closed Loop Feeders with Distributed Generation

This paper investigates voltage and reactive power control in radial and closed loop distribution systems and how the presence of distributed generation (DG) affects the control. Comparative analysis between voltage and reactive power control in radial and closed loop feeders, based on coordination of OLTC, substation capacitors (the shunt capacitors installed at the substation secondary bus) and feeder capacitors (the shunt capacitors located somewhere along the feeder) is presented. The known benefit of closed loop operation is examined in a case study. It is shown that the feeder losses and the voltage fluctuation decrease with the change from radial to closed loop operation. The decrease of voltage fluctuation in the feeder is shown not to reduce the OLTC and capacitor operation. It is also shown that in a certain case closed loop operation can even decrease the maximum allowed DG capacity in the feeders. Further, while it is known that the closed loop operation can defer the distribution line upgrade due to load growth, if the contingency operation is taken into account, the closed loop operation will even earlier request the distribution line upgrade.

The impact of synchronous distributed generation on voltage dip and overcurrent protection coordination

This paper investigates the impact of synchronous distributed generation (DG) in MV network on coordination between overcurrent protection in MV feeder and voltage dip sensed by customer at LV side. DG is expected to support keeping the remaining voltage of a feeder high during voltage dip. DG location affects the level of support that DG can provide. Depending on the location, DG can either increase or decrease short circuit current. Both increasing and decreasing the short circuit current needs readjustment of overcurrent protection, either to ensure the coordination with downstream overcurrent protection, or to maximize DG support during the dip. A voltage dip immunity of a sensitive equipment (SE), which is shown in a voltage-time characteristic, is used to investigate the behaviour equipment during the dip

Various Protection Schemes for Closed Loop Feeders with Synchronous Machine Based Distributed Generation and Their Impacts on Reliability

This paper presents various protection schemes for distribution feeders in a closed loop operation. Firstly, radial and closed loop operation of conventional distribution feeders, what kind of protection schemes can be implemented for the closed loop operation and how those schemes will affect the reliability are briefly investigated. The protection schemes for closed loop conventional distribution feeders are then adopted for distribution feeders with distributed generation (DG) by taking into account the stability of the DG. Cost benefit of each scheme to the reliability of the system is investigated. It is shown that upgrading distribution feeders from radial to closed loop operation without properly upgrading the protection system will decrease the reliability of the system. On the other hand, when the protection scheme is properly upgraded, the closed loop operation will increase the reliability of the system, where the level of upgrade needed will depend on the expected reliability gain.

The impact of the protection scheme of converter connected distributed generation on power system transient stability

In this paper the impact of the protection scheme of converter-connected (power electronic-interfaced) Distributed Generation (DG) on power system transient stability is investigated. Two simulation setups are used for this purpose. In the first setup, a small/simple test system is used and the converter-connected DG is modelled as a practical three-phase full-bridge Voltage Source Converter (VSC). In the latter, a medium-size power system is considered and the converter-connected DG is represented as simple PQ source. In both setups, two possible protection schemes of converter-connected DG are studied. The first one disconnects the DG from the power network during a fault, while the second one keeps the DG connected.