**A New Adaptive Method for Distribution System Protection Considering Distributed Generation Units Using Simulated Annealing Method**

Hamidreza Akhondi and Mostafa Saifali *Sadra Institute of Higher Education Iran* 

#### **1. Introduction**

52 Modeling and Optimization of Renewable Energy Systems

Yu, G.J., Jung, Y.S., Choi, J.Y., Kim, G.S., 2004. A novel two-mode MPPT control algorithm

Zondaga, H.A., Vries, D.W., Helden, W.G.J., Zolingen, R.J.C., Steenhoven, A.A., 2003. The

463.

pp.253–269.

based on comparative study of existing algorithms. *Solar Energy, Vol.*76, pp.455–

yield of different combined PV-thermal collector designs. *Solar Energy*, Vol.74,

Distribution systems usually have radial configuration and have unbalanced operation. Distribution system protection is based on a time over current method. This method includes selection of equipment and settings, placement of equipment, and coordination of devices to clear faults with as little impact on customers as possible. Equipment in distribution protection consists of fuses, reclosers and sectionalizers. Also an over current time inverse relay usually exists inside the distribution substation at feeder outset. In distribution system, the main priorities are to prevent further damage to utility equipment, reliability and power quality (Barker & De Mello, 2003).

The installation of small distributed generation (DG) units at distribution system has many advantages such as energy efficiency, environmental considerations and voltage support. A wide range of power generation technologies are currently in use or under development, these technologies includes: small combustion turbines and micro turbines, small steam turbines, fuel cells, small-scale hydroelectric power, photovoltaic, solar energy, wind turbines and energy storage technologies. Also, Insertion of DG in distribution systems may create technical and safety problems (Brahma, 2001). DG may contribute to increased fault currents, cause in voltage oscillations, decrease or increase losses and interfere in voltage control processes. On the other sides the distribution systems are well designed which could handle the addition of DG if proper grounding, transformers and protection is provided. In fact, all analysis about distribution system occurrence should be reanalyzed as the DG impacts are significant for both planning and operation of distribution networks. The problems associated with protection devices operation and coordination requires special review since they may affect the system security and dependability (Brahma, 2004).

A sample distribution system with DG is shown in Figure 1. In such system DG feed adjacent loads and the system doesn't have radial property. So protection devices must have directional sensitivity in systems with several sources. Fuses, reclosers and sectionalizers don't have directional property while over current relays can equipped with directional element. But displacement of fuses and reclosers with directional over current relays is impossible because of economic considerations. So we need a generalized analysis to distinguish coordination problems of fuse-fuse and fuse-recloser in presence of DG.

A New Adaptive Method for Distribution System Protection

R=0 C.B.1

**3. Inputs and online calculations** 

network.

**4. Short circuit analysis** 

C.B.1

Fig. 2. Distribution system divided into several zones

Main Feeder

Considering Distributed Generation Units Using Simulated Annealing Method 55

BRK

Zone 1 Zone 2 Zone 3

Outline of proposed adaptive protection method is that first, adaptive relay detects the fault in the system and the fault in DG. If the fault occurred in DG, adaptive relay waits until DG protection system detects the fault and isolates DG from distribution system. Then DG circuit breaker sends a signal to adaptive relay so the adaptive relay will do required analysis for new condition of system. If fault is on the system bus bars, adaptive relay performs online short circuit analysis, detects the fault location and faulted zone and sends a trip command to faulted zone circuit breaker and faulted DG circuit breakers. So only the faulted zone is separated from network and other zones continue their normal operations.

A signal indicating the current flow direction in each zone circuit breaker and each DG

The current indicating signal reports the status of circuit breakers in each zone and DG to the mail relay so the relay run the adaptive algorithm based on the network situation.

The main priciples of proposed adaptive algorithm are that first the distribution system data such as loads, line specifications, generator data, transformer data, busbar voltages, circuit beakers status and measured currents are collected and the following online steps are performed in order to specify the fault type and fault location occurred in DG or system busbars. Then a trip command is issued to separate the faulted zone from the

This adaptive method is based on short circuit analysis for all types of occurred faults in different phases. Also the contribution of main feeder and each DG for various fault current in each bus must be determined. Short circuit analysis calculations have to be changed and updated after major changes in load, DG or system configuration. So after each change, short circuit analysis is performed online and required information will be send to adaptive

C.B.2 C.B.3 C.B.4

C.B.2

The following measurements are used for the proposed algorithm: RMS value of three phase current in each DG and main source.

circuit breaker (Chowdhury & Crossley ,2009).

relay in order to analysis and Prescription (Sukumar ,2001).

BRK

Zone 4

C.B.6

BRK

Zone 5

C.B.5

BRK

Fig. 1. Sample Distribution System with DG

In this paper, the effect of DG insertion into a distribution network on protection system operation is evaluated by means of short circuit analysis and protective device coordination. In the other words, this paper describes the characteristics of distribution feeder protection and DG interconnection protection, respectively. A new adaptive method is presented based on simulated annealing optimization method for distribution protection considering DG. Simulation results show the effectiveness of the proposed method.

#### **2. Proposed methodology**

As it mentioned in previous section, distribution system misses its radial nature in presence of distributed generations. So the protective devices may lose their coordination and proper operation. To keep the coordination of protective devices, it is necessary to separate distributed generations after each fault even for transient fault. The ideal for each protection scheme is that only the faulted section is separated form system and other parts maintain their operations. It should be noted that the coordination of fuse-fuse, fuse-recloser, fuserelay and relay-recloser diminish considering the loss of radial nature of distribution network after DG insertion. So the best approach is to divide the distribution system into several zones as shown in Figure 2. These zones should be separated by circuit breakers. The breakers must have the ability of system synchronization and frequent switching because of receiving a signal from main relay located in the substation.

Fig. 2. Distribution system divided into several zones

Outline of proposed adaptive protection method is that first, adaptive relay detects the fault in the system and the fault in DG. If the fault occurred in DG, adaptive relay waits until DG protection system detects the fault and isolates DG from distribution system. Then DG circuit breaker sends a signal to adaptive relay so the adaptive relay will do required analysis for new condition of system. If fault is on the system bus bars, adaptive relay performs online short circuit analysis, detects the fault location and faulted zone and sends a trip command to faulted zone circuit breaker and faulted DG circuit breakers. So only the faulted zone is separated from network and other zones continue their normal operations.

## **3. Inputs and online calculations**

54 Modeling and Optimization of Renewable Energy Systems

load

load

In this paper, the effect of DG insertion into a distribution network on protection system operation is evaluated by means of short circuit analysis and protective device coordination. In the other words, this paper describes the characteristics of distribution feeder protection and DG interconnection protection, respectively. A new adaptive method is presented based on simulated annealing optimization method for distribution protection considering DG.

As it mentioned in previous section, distribution system misses its radial nature in presence of distributed generations. So the protective devices may lose their coordination and proper operation. To keep the coordination of protective devices, it is necessary to separate distributed generations after each fault even for transient fault. The ideal for each protection scheme is that only the faulted section is separated form system and other parts maintain their operations. It should be noted that the coordination of fuse-fuse, fuse-recloser, fuserelay and relay-recloser diminish considering the loss of radial nature of distribution network after DG insertion. So the best approach is to divide the distribution system into several zones as shown in Figure 2. These zones should be separated by circuit breakers. The breakers must have the ability of system synchronization and frequent switching because of

load

DG

R=0

load

DG

load

R=0

R=0

DG

R=0

Main Feeder

R=0

Fig. 1. Sample Distribution System with DG

**2. Proposed methodology** 

DG

load

R=0

DG

Simulation results show the effectiveness of the proposed method.

receiving a signal from main relay located in the substation.

The following measurements are used for the proposed algorithm:


The current indicating signal reports the status of circuit breakers in each zone and DG to the mail relay so the relay run the adaptive algorithm based on the network situation.

The main priciples of proposed adaptive algorithm are that first the distribution system data such as loads, line specifications, generator data, transformer data, busbar voltages, circuit beakers status and measured currents are collected and the following online steps are performed in order to specify the fault type and fault location occurred in DG or system busbars. Then a trip command is issued to separate the faulted zone from the network.
