Using the Summation Function

How can I use the Summation Function in PTW ?

The Protective Device Function in PTW v6.5 contains new features for modeling additional functions, such as summation, that can be utilized in Arc Flash Evaluation.
The following provides a brief description of implemented concept for the summation function, how it can be used, and how to apply it in a study.

General Implemented Concept

1. The summation function in PTW is similar to a bus differential which can sum up the SC contribution currents vectors (magnitude and angle) caused by a fault and passed through multiple devices already modeled in the connected branches to the fault location.

2. Since the actual CTs for sensing and the conversion of the fault currents are not yet available, the protective devices available in each branch will act in place of the CTs and the program will internally account for the SC current summation.

3. The actual characteristics of the bus differential relay cannot currently be modeled in Captor. However, a generic TCC representing any adjustable pickup and delay can be used instead to represent the trip time for the fault.

4. Based on the above, a protective device is needed to be inserted in each of the branches connected to the bus as the location of fault to define the protected zone. Every device type needs to be set as Summation through the Function button in Captor or the Component Editor and linked to the library to represent the generic TCC of the device.

The following example will better describe the use and application of the summation function.


Figures 1 and 2 represent a sample dual source distribution system containing only the phase Over Current Type Function while Figure 3 displays the arc flash results for the switchgear bus (BUS-SWG) connecting the generators and motor loads without any summation function or bus differential.

The following steps can be used to add summation function to the existing overcurrent phase function of the PD-GEN-1 relay. This relay will be used together with all other relays (PD-GEN-2, PD-1, and PD-2) as the reference for the sensed current by each of these CTs.

1. Select the PD-GEN-1 device in the Captor TCC drwing (Figure 4) then click the Function button to display the Protection Functions.

2. Click the New button and type in Summation under the Function Name column. Select Summation from the Type pull-down menu (Figure 5).