Versions Compared


  • This line was added.
  • This line was removed.
  • Formatting was changed.


The directional overcurrent relay (50-51-67) trips if and only if the fault current magnitude is above the threshold (50-51) and it is in a specific direction (67). The direction can be forward or reverse depending on the type of fault and type of directional element which is activated.

This document focuses on the 67 element: part of the 50-51-67 model and the directional element of the overcurrent relay. For information regarding the overcurrent model or the measurement block used in both 5051 and 505167 models, refer to 50-51 relay documentation.

The 67 model determines the direction of the fault current based on the phase difference between the phase currents and phase-to-phase voltages (67P) or the phase difference between zero-sequence current (derived from neutral current) and either zero-sequence voltage or ground current (67N). The direction enables the overcurrent relay to trip or acts as a blocking signal.

The 50-51-67 or Directional Overcurrent Relay trips whenever the monitored current exceeds the predefined setting and is in the desired direction. This is true for both phase overcurrent and neutral overcurrent.

titleTable of Content

Table of Contents

The figure below shows the concept of how the relay operates.

The direction discrimination principle is based on phase angle comparison between a set of phasors, one of which is used as a reference. The reference value is called the polarizing quantity and the value which is being compared is the operating quantity. In the case of 67, the operating quantity is always the fault current. By shifting the quantities by a specified value called the Element Characteristic Angle (ECA) or Relay Characteristic Angle (RCA), the model can determine the operating regions of the relay in terms of fault current direction. The directional element can act as a tripping mechanism or blocking for the overcurrent model.

Directional Elements

The model contains two directional elements: Phase Directional (67P) and Neutral Directional (67N).

67P Phase Directional Overcurrent Element

The operating quantity in 67P element is the phase current and the polarizing quantity is the line-to-line voltage. During a fault, the phase voltage is low so to be able to determine the direction, the line-to-line voltage is considered as a reference . The voltage is shifted by an amount of the ECA specified by the user to find the operating regions of the relay. The phase difference between the operating quantity and polarizing quantity is compared with 90 degrees and it is determined whether the fault current is in forward (trip) or reverse (block).

If phase-to-phase voltage drops to lower than 0.1 pu, the voltage memorized from 3 cycles ago is used for direction discrimination. The user has a choice of sending a blocking signal when voltage memory expires by enabling or disabling a setting (Block after voltage memory expiration) in the relay. When the setting is enabled, the directional element will block the phase overcurrent operation under directional control when voltage memory expires. If it is disabled, the phase overcurrent functionality can trip under directional control when voltage memory expires.

If phase current is higher than the threshold of 0.05 pu and based on the directional discrimination, the output of the 67 element can be forward (1) or reverse (0).

Forward direction is used for tripping the phase overcurrent and reverse is used for blocking. So, the overcurrent relay trips if a phase fault current is above a certain threshold and the direction is in forward [1].

67N Neutral Directional Overcurrent Element

The 67N element has one operating quantity which is the zero-sequence current:

                                                          I0 = (1/3) * IN = (1/3) * (IA+ IB+ IC)

The positive sequence current acts as a restraint for better relay performance and is subtracted from the zero-sequence current with a factor of K. So, the operating current would be:

                                                          Iop = 3 * (I0 - I1 * K) , K = 1/16

K is recommended to be set to 1/16 [2] for neutral directional overcurrent settings but can be changed.

Based on the polarizing quantity, there are different polarization modes for 67N. If Voltage Polarization is chosen by the user, the polarizing quantity is the zero-sequence voltage:

                                                         Polarizing Quantity = Vpol = V0 = (1/3) * VN = (1/3) * (VA + VB + VC)

If Current Polarization is chosen, the polarizing quantity is the ground current which can be taken from the ground CT. (IG)

                                                          Polarizing Quantity = Ipol = IG

If Dual Polarization is chosen, both polarizing quantities are used for direction discrimination.

Direction discrimination is the same principle as it is for 67P. Based on the phase angle difference between the polarizing and operating quantities, direction of the fault current is determined.

Characteristic Angle (ECA) is used in voltage polarization. The user can specify the pickup current and limit angles which are used for directional discrimination in both forward and reverse directions. It should be noted that the pickup value is separate than the one used for 50N or 51N and is typically a very low value. The phase angle difference between the operating quantity and polarizing quantity is compared with Forward Limit Angle and Reverse Limit Angle which determines the operating regions of the 67N element.  

                                                          if angle difference < forward limit angle => forward direction (1)

                                                          if angle difference < reverse limit angle => reverse direction (1)

Because of this method, there are two outputs for 67N. One shows the direction in forward which can be 0 or 1 and the other shows the direction in reverse which also can be 0 or 1. There are non-operation zones which the output for both forward and reverse direction is zero. So, if the output for reverse direction is zero, it does not mean the output for forward direction is 1 and vice versa.

There are areas where the direction could be forward for current polarization but reverse for voltage polarization. In Dual polarization mode, the forward direction is considered as the main direction of the 67N element. So if both forward and reverse directions are true, the 67N output shows 1 for forward and 0 for reverse.

The output of the neutral directional element is always a tripping signal which is sent to the neutral overcurrent element. The user can choose whether the tripping signal is sent from forward direction or reverse. This gives more options to users.

The overcurrent relay trips if a neutral fault current is above the threshold (for 50-51N) and its direction is either forward or reverse [3].

Table below summarizes the different directional elements in 67.

Relay Type

Polarization mode

Operating Quantity

Polarizing Quantity






One output:

1: FWD

0: REV




I0 ∠ ECA-V0

Two outputs:

0 or 1: FWD

0 or 1: REV




I0 ∠ ECA or I0-V0 or IG

Mask and Parameters

General Parameters

NameDescriptionUnitVariable = {Possible Values}
FrequencyThe frequency of the measured current signals. Both 50 and 60 Hz are supported within the model.HzFreq_param= {50, 60}
Base currentBase value for currentAIbase_param = [1, 1e5}
Base voltageBase value for voltageVVbase_param = [1, 1e8}

Directional Overcurrent Parameters

NameDescriptionUnitVariable = {Possible Values}
Enable phase directional 67PEnable the use of 67P for control of phase overcurrent-Dir_Enabled_67P_param =  {0, 1}
ECA (67P)ECA angle for 67PdegECA_67P_param =  [0, 359}
Blocking signal when voltage memory expiresEnable sending a blocking signal when voltage memory expires in 67P-Block_Vmem_param =  {0, 1}
Enable neutral directional 67NEnable the use of 67N for control of neutral overcurrent-Dir_Enabled_67N_param =  {0, 1}

Choose directional element for tripping

Select either forward or reverse current as tripping signal for neutral overcurrent control-

DIR_67N_param = {1, 2}

Forward (1)Forward direction
Reverse (2)Reverse direction
Positive sequence restraint factor (K)The factor used for positive sequence restraint in calculating the operating current for neutral directional overcurrent 67N-K_param =  [0, 0.0625}
ECA (67N)ECA angle for 67NdegECA_67N_param =  [-90, 90}
Polarization modePolarization mode for 67N-Pol_Mode_param =  {1, 2, 3}
Current (1)Current polarization
Voltage (3)Voltage polarization
Dual (2)Dual polarization
Enable ground calculation (current polarization)Enable ground current and voltage calculations that are used for current polarization-EnableGround_param =  {0, 1}
Forward direction pickup currentPickup current for forward directional discriminationpuI_FWD_PKP_param =  [0.002, 3}
Reverse direction pickup currentPickup current for reverse directional discriminationpuI_REV_PKP_param =  [0.002, 3}
Forward direction limit angleLimit angle for forward directional discriminationdegFWD_LIM_ANG_param =  [40, 90}
Reverse direction limit angleLimit angle for reverse directional discriminationdegREV_LIM_ANG_param =  [40, 90}

Inputs, Outputs and Signals Available for Monitoring


IabcThree-phase currents
VabcThree-phase voltages
IGGround current taken from the ground CT
VGGround voltage taken from the ground VT
ResetThe reset signal for the relay. The relay will be reset when this signal becomes 1


QThe output of directional overcurrent relay. By default, it is 0, if an overcurrent scenario is detected, it becomes 1
Q_hThe complementary value of Q


Iabc(0,1,2)Three phase currentsA
Vabc(0,1,2)Three phase voltagesV
IGGround currentA
VGGround voltageV
QDirectional overcurrent relay output 50-51-67-
Q_hComplementary of Q-
ResetReset signal for the relay-
S_50P(A,B,C)Output of three phase overcurrent 50P-
S_50NOutput of neutral overcurrent 50N-
S_51P(A,B,C)Output of three phase inverse overcurrent 51P-
S_51NOutput of neutral inverse overcurrent 51N-


Output of three phase directional overcurrent 67P-
S_67NOutput of neutral directional overcurrent 67N-

Typical Values for Parameters

The parameter section shows the possible values for each parameter. This section specifies typical values for a few parameters which would be useful as a start to work with the relay model. These values would change to fit the situation of the 50-51-67 relay model so they cannot be taken as sole values for each parameter.

NameDescriptionUnitTypical Values
ECA (67P)ECA angle for 67Pdeg30, 45, 60, 85
ECA (67N)ECA angle for 67Ndeg-80, 80
Forward direction pickup currentPickup current for forward directional discriminationpu0.02
Reverse direction pickup currentPickup current for reverse directional discriminationpu0.02
Forward direction limit angleLimit angle for forward directional discriminationdeg65
Reverse direction limit angleLimit angle for reverse directional discriminationdeg65


[1] GE Industrial Systems, “D60 Line Distance Relay: UR Series Instruction Manual”, Section 5.5.7.e: Phase Directional Overcurrent, (2009 GE Multilin)

[2] Bogdan Kasztenny, Dave Sharples, Bruce Campbell, Marzio Pozzuoli, “Fast Ground Directional Overcurrent Protection: Limitations and Solutions”, Page 16, (2000 GE Grid Solutions)

[3] GE Industrial Systems, “D60 Line Distance Relay: UR Series Instruction Manual”, Section 5.5.8.d: Neutral Directional Overcurrent, (2009 GE Multilin)