Table of Contents

## What do you understand by concept of GMR and GMD?

GMD & GMR stands for Geometrical Mean Distance and Geometrical Mean Radius. In GMD we take the Geometrical Mean of distances between the strands of two Transmission Lines while in GMR, Geometrical Mean of distances between the stands of a single composite conductor are calculated.

**How do you calculate GMD and GMR?**

Consider a 3-ph unsymmetrical line with distances b/w phases equal to D1,D2,D3 and solid conductor of radius r . Then GMD=[D1D2D3]^(1/3) and GMR= 0.7788r for the calculation of L , line inductance and GMR =r , for the calculation of C , line Capacitance.

**How do you find the GMR of a conductor?**

- Concept:
- GMR:
- GMR = [{D11 × D12 × D13} {D21 × D22 × D23} {D31 × D32 × D33}]1/9.
- D12 = Distance between conductor 1 and 2.
- D23 = Distance between conductor 2 and 3.
- D32 = Distance between conductor 4 and 3.
- D11, D22, D33 = r’ = GMR of conductor 1, 2 and 3 respectively.
- D11 = e-0.25R = 0.7788 R.

### What is mutual GMD?

The mutual-GMD is the geometrical mean of the distances form one conductor to the other and, therefore, must be between the largest and smallest such distance. In fact, mutual- GMD simply represents the equivalent geometrical spacing.

**How is self GMD calculated?**

In the above equation, Ds = self-GMD or GMR = 0.7788r. GMR depends upon the shape of the conductor and the size of the conductor. GMR is independent of spacing between the conductors.

**What is Ferranti effect in transmission line?**

In electrical engineering, the Ferranti effect is the increase in voltage occurring at the receiving end of a very long (> 200 km) AC electric power transmission line, relative to the voltage at the sending end, when the load is very small, or no load is connected.

#### What is the difference between GMD and GMR in transmission lines?

In GMD we take the Geometrical Mean of distances between the strands of two Transmission Lines while in GMR, Geometrical Mean of distances between the stands of a single composite conductor are calculated. Let us assume two composite conductors used in Transmission Line as shown in figure below.

**How to calculate the GMD of a solid conductor?**

For getting the GMD, first we need to calculate the distance between the strands of Go and Return conductors. Geometrical Mean Radius of a solid conductor or a strand of radius R is defined as the factious radius R’ having no internal flux linkage but having the same inductance as the original conductor of radius R.

**What is the meaning of GMR of conductor?**

The Geometrical Mean Radius GMR of conductor is taken in such a way that inductance of conductor due to external flux linking becomes equal to the original inductance LA. This means Thus Geometric Mean Radius GMR of a conductor is that fictitious radius which do not has any internal flux linkage but only have external flux linkage.

## What is GMR (geometrical mean radius)?

Geometrical Mean Radius of a solid conductor or a strand of radius R is defined as the factious radius R’ having no internal flux linkage but having the same inductance as the original conductor of radius R. For calculating GMR, first we find the distance between the individual strands.