Protection relay

1. A protection relay for protecting an electric system, comprising:

a receiver configured to receive a time multiplier value;

a calculator configured to calculate, with the received time multiplier value, an inverse definite time dependency having an exponentiation function, wherein the dependency defines a relationship between an excitation level of an input signal to the relay and an operating time of the relay;

a shifter configured to shift the dependency to a predefined calculation space; and

an applier configured to apply, during execution, the dependency shifted to the predefined calculation space when determining an operating condition of the relay.

2. The protection relay as claimed in claim 1 , wherein the shifter is configured to shift the dependency to the predefined calculation space by calculating a new time multiplier value to define a new dependency; and

the calculator is configured to calculate and store in a lookup table, calculation values representing the new dependency, which calculation values are calculated as a function of an excitation level.

3. The protection relay as claimed in claim 1 , wherein the applier is configured to:

apply, during execution, a calculation value from the lookup table when an excitation level falls between the excitation levels applied in the lookup table;

apply a maximum calculation value of the lookup table when an excitation level during execution exceeds the maximum calculation value; and

apply a minimum calculation value of the lookup table when an excitation level during execution undershoots the minimum calculation value.

4. The protection relay as claimed in claim 1 , wherein:

the receiver is configured to receive a predefined maximum operating time limit for the relay,

the calculator is configured to calculate an excitation level leading to the maximum operating time limit, and

the shifter is configured to shift all the values of the dependency such that the excitation level, at which the maximum operating time setting limit is achieved, is moved to a predefined excitation value.

5. The protection relay as claimed in claim 1 , wherein:

the receiver is configured to receive a predefined maximum operating time limit and/or a predetermined minimum operating time for the relay,

the calculator is configured to add a margin to the maximum operating time and/or to the minimum operating time, and

the calculator is configured to apply the maximum operating time and/or the minimum operating time, to which the margin has been added, when calculating calculation values to the lookup table.

6. The protection relay as claimed in claim 1 , wherein the shifter is configured to:

identify an upper excitation level and a lower excitation level of the dependency;

shift the dependency between the upper excitation level and the lower excitation level; and

the calculator is configured to calculate, between the upper limit and the lower limit, a plurality of calculation values as a function of the excitation by applying a predetermined formula and store the plurality of values in an indexed look up table to be applied during execution of the relay.

7. The protection relay as claimed in claim 1 , wherein the relay comprises:

a monitor configured to monitor an input signal during execution;

a determiner configured to determine an excitation level of the input signal;

a modifier configured to modify the excitation level determined from the measured input signal;

a fetcher configured to fetch a calculation value corresponding to the modified excitation level from a look up table;

a performer configured to perform an inverse definite time integration based on the calculation value and a predetermined fixed term; and

a checker configured to check, based on the integration, if the operate condition of the relay is fulfilled.

8. The protection relay as claimed in claim 1 , wherein the dependency is an exponential function.

9. The protection relay as claimed in claim 1 , wherein the dependency can be modelled as a straight in a linear-logarithmic space, wherein the linear x-axis depicts an excitation level and the logarithmic y-axis the operating time of the relay.

10. The protection relay as claimed in claim 1 , wherein the time multiplier value is at least 10.

11. The method of protecting an electric system, comprising:

receiving a time multiplier value;

calculating, with the received time multiplier value, an inverse definite time dependency having an exponentiation function wherein the dependency defines a relationship between an excitation level of an input signal to the relay and an operating time of the relay,

shifting the dependency to a predefined calculation space; and

applying, during execution, the dependency shifted to the predefined calculation space when determining an operating condition of the relay.

12. The method as claimed in claim 11 , wherein the method comprises:

identifying an upper excitation level and a lower excitation level of the dependency;

calculating, between the upper limit and the lower limit, a plurality of calculation values as a function of the excitation by applying a predetermined formula; and

storing the plurality of values in an indexed look up table to be applied during execution of the relay.

13. The method as claimed in claim 11 , wherein the method comprises:

receiving a predefined maximum operating time limit for the relay;

adding a margin to the maximum operating time; and

applying the maximum operating time, to which the margin has been added, when calculating calculation values to the lookup table.

14. The method as claimed in claim 11 , wherein the method comprises:

monitoring an input signal during execution;

determining an excitation level of the input signal;

modifying the excitation level determined from the measured input signal;

fetching a calculation value corresponding to the modified excitation level from a look up table;

performing inverse definite time integration based on the fetched calculation value and a predefined fixed term; and

checking, based on the integration, if the operating condition is fulfilled.

15. A protection relay for protecting an electric system, comprising:

means for receiving a time multiplier value;

means for calculating, with the received time multiplier value, an inverse definite time dependency having an exponentiation function, wherein the dependency defines a relationship between an excitation level of an input signal to the relay and an operating time of the relay;

means for shifting the dependency to a predefined calculation space; and

means for applying, during execution, the dependency shifted to the predefined calculation space when determining an operating condition of the relay.

16. A non-transitory computer program product includes a computer usable medium having a computer readable program code recorded therein, wherein when said computer program product is in communicative contact with a processor, the program code causing the processor to execute the steps of:

receiving a time multiplier value;

calculating, with the received time multiplier value, an inverse definite time dependency having an exponentiation function wherein the dependency defines a relationship between an excitation level of an input signal to the relay and an operating time of the relay;

shifting the dependency to a predefined calculation space; and

applying, during execution, the dependency shifted to the predefined calculation space when determining an operating condition of the relay.