been introduced as a solution for mis-coordination and false tripping issues associated with DG penetration

increase. In this paper, this approach is highlighted, and its performance in different operating modes of the

DG-connected grid is evaluated. Genetic algorithm (GA), and gray wolf optimization (GWO) have been used

to provide optimized values of the time multiplier setting (TMS) of the DOCR scheme. Different faults at

different locations with different DG locations and sizes are studied. The international electrotechnical

commission (IEC) micro-grid benchmark and different DG units are modeled with MATLAB Simulink and

ETAP software to carry out and test all these operating modes and evaluate this scheme. The ability of this

scheme to maintain the coordination between the forward and reverse main and backup relays for each fault

location is focused on in this study.

Increasing the DG penetration is always

accompanied not only by increasing the short-circuit

current but also by an obvious change in the

relaying fault current either by increasing or

decreasing in magnitude or change in direction

according to the DG connection point relative to the

relaying points. Since the OCR operation is based

only on the fault current magnitude measured at the

relaying points, the DG connection is strongly

from the upstream to the downstream points of the

radial network. Due to the DG connection to the

distribution network, its radial nature has been lost,

the challenges concerning short circuit capacity, and

protection coordination has been introduced and its

impacts on the protection system have been

overall relay operating time for primary and backup

scenarios, all these methods were introduced in the

works of literature for DG impacts mitigations on

the OCR scheme coordination, [2], [9]. From these

suggested solutions, the optimization of the

directional OCR settings has been introduced by

many researchers recently to overcome the

protection coordination problems due to

bidirectional fault currents and to provide an

adaptive OVR setting, [10], [11], [12], [13], [14],

used for comparative analysis, the authors just

focused on the main primary and backup relays for

each fault location, ignoring the overall backup

relays that the reverse fault current is passed

through. Adaptive Clonal selection algorithm of the

artificial immune system(AIS) is used in, [12], to

provide the optimized TMSs, and the novel

optimization solvers such as modified PSO,

teaching-learning, GWA, moth-flame, and PSO

algorithms were used in [13], GA, PSO, and

(PSO) in, [15], Artificial bees colony (ABC) is

employed in, [16], Honey Bee algorithm is used in,

[17].

with minimizing the overall operating time of the

relaying protection scheme without regard to the

performance of all the backup relays by which the

fault current was sensed. Reducing the overall

computational time by using a modern optimization

tool is not the main objective of this study, but the

scheme to cover all the fault scenarios has been

highlighted in this paper using GA, and GWA.

standard and non-standard curves of directional and

non-directional OCR schemes that were introduced

by several pieces of literature are tested for different

operation modes of DG-connected multi-infeed

 The constraints related to the suitable margin of

required to implement an adaptive protection scheme

that tracks the topology changes of the network with

Table 1. The optimized values of TMS in the case of

Fig. 3: Optimal relays setting curves for DG

connection at Bus 2 scenario

this case, its influence is strong in the case of DG

connection at Bus4 (see Fig. 4), and the selectivity

of the relaying scheme is completely lost as in Fig.

5. For example, R3, and R4 lead the main and

different buses of the IEC network. To provide a

selective relaying scheme, 15 relays (R1-R15) are

used to cover the new network topology and it

should be coordinated as in Table 2. The

coordination between relays must be updated to

meet the expected changes in the fault current

magnitude and direction based on DG location. The

updating process comprises updating TMS values

for the forward existing relays (R1-R6) and the new

installation relays (R7-R15). The optimized values of

achieved as in Table 3.

Fig. 6: IEC modified model with connecting 4-DGs

and directional overcurrent relay.

relays, the backup relays R8, and R10 have tripped

faster than the main one R7 preventing the DG

penetration in the reverse fault current, then the fault

current measured at R7 will be decreased and its

tripping time will be increased, and the coordination

problem could be aggravated. This problem is

brightly indicated in the intersection of the main and

backup relays setting curves at high fault current

rating as in Fig. 7. Moreover, the problem of

coordination between relays is strongly manifested

points are changed and its operation time is shifted

on its setting curve as a result the pre-setting CIT

could not be achieved for the forward and reverse

direction relays.

6.5 Fault at the End of Line 5

From Table 9, it can be noticed that R5 and R2 could

keep the CTI constraints, but unfortunately, R8

could not, so the coordination could not be achieved

for all relays. In contrast, the selectivity between the

reverse current relays has been completely lost since

test if the constraints are achieved or not for all fault

locations. Faults [ F1-F2-F3-F4-F5] at feeder sections

[ Line 1-Line 2- Line 3- Line 4- Line 5]

respectively.

forward current relays to keep the preset CTI is

larger than the reverse current relays (R2, R3, and

R4 are satisfied the coordination constraints), the

DGs connection points. The other relays satisfy the

constraints sometimes and are violated at other

times. It can be concluded that the reverse relays

that are located between the DGs connection points

are the ones violating coordination constraints.

From equation 3, it can be noticed that each relay is

coordinated multi-times with the main relay for

different fault locations, this is the main cause of the

confusion of DOCR scheme selectivity. So, this

method could not provide a complete solution for

non-standard IDMT equation.

For any reason such as maintenance, or fault cases,

the utility infeed will be lost, and the IEC micro-grid