Calculations > Protection

The protection analysis examines the correctness of type and parameter specifications. Vision checks the thermal load of branches and the protection selectivity. For this Vision automatically creates short circuits on user specified nodes, by using the fault analysis method. The calculations may be verified in detail by executing a fault analysis study.

Also faults in cables and connections can be simulated. In that case, in the Options the Cable calculation steps must be non-zero. It defines the number of equidistant short-circuit places in each cable or connection. An option has been added to simulate short-circuits close to the from and to nodes (1% and 99% of distance).

Also the consequences of a protection or circuit breaker operating failure can be analysed. If this option is switched on, extra calculations will be made and extra results will be visible.

Vision has four types of protection calculations:

Calculation	Fault location	Fault type	Fault impedance	Result
One fault	One selected object	One fault type	One fault impedance	Details of nodes and branches
Simulation	Multiple selected objects	Multiple fault types	One fault impedance	Details of nodes and summary of branches
Selectivity	Multiple selected objects	Multiple fault types	A range of fault resistances	Selectivity of nodes and branches
Analysis	Multiple selected objects	A range of fault types	Three fault resistances (fixed)	Undesired events

Fault location:

the user selects one or multiple fault locations

Fault type:

short-circuit between phase and ground, between two phases, between two phases and ground of between three phases; a range of fault types is specified in the Options, at: Calculation | Network analysis | Voltage dip analysis and protection analysis.

Fault impedance:

resistance and reactance on the fault location; to be specified by the user; a range of fault resistances is specified in the Options, at: Calculation | Protection; the three fault resistances for the protection analysis are fixed

One fault (Simulation)

The protection sequence can be evaluated for a fault on a single object/location. This is principally the same calculation as the Simulation calculation, but always executed for one fault on one specific object/location only. With this calculation, many detailed voltage and current results are available during the sequences of the protection actions.

The results are:

•Protection switching sequence details

•Short-circuit location short-circuit currents during the protection switching sequence (maximum value for the 3 phases)

•Node voltages during the protection switching sequence (minimum value for the 3 phases)

•Branch and element currents during the protection switching sequence (maximum value for the 3 phases)

•Branch I²t

•Faulted node I²t

The colour indications are as follows:

•Nodes, branches and elements that are thermally overloaded: too high colour

•Short-circuit indicators that tripped: attention colour

•Protection devices that have picked up: attention colour

•Protection devices that have tripped: trip colour

•Circuit breakers and fuses that have switched off: out colour

This analysis is input by the user as follows:

•select the object for wich the protection has to be evaluated

•choose Calculation | Calculation | Protection | One fault

•choose fault type

•specify fault impedance, like in Fault analysis

•leave the form with OK.

Simulation

Executing a simulation analysis the next steps are carried out:

•a specified fault is created on a specified node or in a branch

•hereafter all network currents are calculated

•next all protection switch off times are determined

•the first tripping protection opens the switch

•the network currents are determined again

•if necessary and available the next switch opens

•the process is repeated until the fault is isolated.

This analysis is input by the user as follows:

•select the nodes for wich the protection have to be evaluated

•choose Calculation | Calculation | Protection

•choose the fault types

•specify fault impedance, like in Fault analysis

•specify the option to include protection or circuit breaker operating failure

•leave the form with OK.

Selectivity

Executing a selectivity analysis the next steps are carried out:

•for a specified fault type several faults, each having a different fault impedance (see: Options), are created on the specified nodes

•for each fault all network currents are calculated

•for all protection devices all switch off times are calculated and saved

•the tripped switches are opened

•then all changed network currents and changed switch off timed are calculated

•the tripped switches are opened and the previous step us repeated until the short circuit has been switched off

Result are current and time curves generated by various fault impedances. Presented in graphs, these curves provide insight in the protection selectivity.

This analysis is input by the user as follows:

•select the nodes for wich the protection have to be evaluated

•choose Calculation | Calculation | Protection

•choose the fault types

•leave the form with OK.

Analysis

The protection analysis function analyses the protection settings, in combination with the possibility that they refuse to operate. See: Protection analysis.

User settings

Cable calculation steps

The number of equidistant places within the cable/line where short circuits are to be simulated, can be specified with the number of cable calculation steps. An option has been added to simulate short-circuits close to the from and to nodes (1% and 99% of distance).

Protection: Calculation

Protection: Calculation