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 SPECIFICATION  Approval item: 

Overview

switch objects provide a means to electrically disconnect two portions of the power system model. The switch is a subclass of link objects, so it will connect two node-based objects on the system. Operations on the switch will either allow current flow between these node objects, or prevent it.

GLM Inputs

The switch is a very basic device. A minimal switch, accepting the default of being closed, would look like:

 object switch {
 	phases ABC;
 	name connecting_switch;
 	from node1;
 	to node2;
 }

The switch-specific, full GLM-accessible-properties object would be:

 object switch {
 	phases ABC;
 	name connecting_switch;
 	from node1;
 	to node2;
 	status CLOSED;
 	switch_resistance 0.0001 Ohm;
 }

It is useful to note that the status field will manipulate all of the phases on the switch. i.e., this device only operates in banked mode - if individual phase switching is needed, individual switch devices would need to be instantiated for each phase.

All standard link properties are inherited as well, and are not listed here (e.g., current and power flow through the switch).

Details on the properties are outlined in Table 1. Note that although some of these are defined in the base link class, they're also listed here for completeness.

Table 1 - Switch properties
Property Type Definition
phases set Phases the switch will conduct across. All switch operations will affect all of these phases (only operates in a banked configuration)
name char1024 Base GLD property - name of the object for easier debugging and reference
from object Base link property - name of the node-based object on one end of the switch
to object Base link property - name of the node-based object on the opposite side of the switch
status enumeration Base link property - can be OPEN (from and to are disconnected) or CLOSED (from and to are connected). By default, the device starts CLOSED. All phases present are influenced by this (only banked operation).
switch_impedance complex Defines the impedance (per-phase) of the switch, when in the CLOSED state. Defaults to the default_resistance property of the powerflow module for both the real and reactive components.
switch_resistance double Defines just the real portion (per-phase) of switch_impedance. If unspecified, defaults to default_resistance, as dictated by switch_impedance above.
switch_reactance double Defines just the reactive portion (per-phase) of switch_impedance. If unspecified, defaults to default_resistance, as dictated by switch_impedance above.

Model Implementation

Implementation for the two different solver method (FBS and NR) are similar, but different enough that the details are outlined here. Switches are assumed to just connect direct phases. e.g., phase A of from to phase A of to; no phase-switching or other configurations are supported.

FBS

The Forward-Backward Sweep method implementation follows the standard line equations from Distribution System Modeling and Analysis, by William Kersting:

[math]\mathbf{V}_{to}=\mathbf{A}\mathbf{V}_{from}-\mathbf{B}\mathbf{I}_{to}[/math]
[math]\mathbf{V}_{to}=\mathbf{d}\mathbf{V}_{from}-\mathbf{b}\mathbf{I}_{from}[/math]
[math]\mathbf{V}_{from}=\mathbf{a}\mathbf{V}_{to}+\mathbf{b}\mathbf{I}_{to}[/math]
[math]\mathbf{I}_{to}=\mathbf{-c}\mathbf{V}_{from}+\mathbf{d}\mathbf{I}_{from}[/math]
[math]\mathbf{I}_{to}=-\mathbf{c}\mathbf{V}_{from}+\mathbf{a}\mathbf{I}_{from}[/math]
[math]\mathbf{I}_{from}=\mathbf{c}\mathbf{V}_{to}+\mathbf{d}\mathbf{I}_{to}[/math]

The matrices [math]\mathbf{A},\mathbf{B},\mathbf{a},\mathbf{b},\mathbf{c},[/math] and [math]\mathbf{d}[/math] must be defined. By Kersting's equations, [math]\mathbf{A}=\mathbf{a}^{-1}[/math] and [math]\mathbf{B}=\mathbf{a}^{-1}\mathbf{b}[/math].

For OPEN states, the relevant phases of the diagonal elements of the matrices are zero:

[math]\mathbf{A}=0.0[/math]
[math]\mathbf{B}=0.0[/math]
[math]\mathbf{a}=0.0[/math]
[math]\mathbf{b}=0.0[/math]
[math]\mathbf{c}=0.0[/math]
[math]\mathbf{d}=0.0[/math]

For CLOSED states, the relevant phases of the diagonal elements of the matrices are:

[math]\mathbf{A}=1.0[/math]
[math]\mathbf{B}=[/math]switch_impedance
[math]\mathbf{a}=1.0[/math]
[math]\mathbf{b}=[/math]switch_impedance
[math]\mathbf{c}=0.0[/math]
[math]\mathbf{d}=1.0[/math]

NR

The Newton-Raphson method implementation is simplified into four matrices. The specifics of their use are detailed, but equations will be omitted, for brevity.

[math]\mathbf{Y}[/math] - admittance matrix - used in the powerflow solution
[math]\mathbf{b}[/math] - impedance matrix - used for current and power calculations
[math]\mathbf{a}[/math] - voltage ratio matrix - used in some fault and standard current calculations
[math]\mathbf{d}[/math] - voltage ratio matrix - used for current and power calculations

For OPEN states, the relevant phases of the diagonal elements of the matrices are zero:

[math]\mathbf{Y}=0.0[/math]
[math]\mathbf{b}=0.0[/math]
[math]\mathbf{a}=0.0[/math]
[math]\mathbf{d}=0.0[/math]

For CLOSED states, the relevant phases of the diagonal elements of the matrices are:

[math]\mathbf{Y}=\frac{1}{Z_s}[/math]
[math]\mathbf{b}=Z_{s}[/math]
[math]\mathbf{a}=1.0[/math]
[math]\mathbf{d}=1.0[/math]

where [math]Z_{s}[/math] is the value of switch_impedance.

Whenever a switch state changes (OPEN to CLOSED and vice-versa), the switch will also set the powerflow global NR_admit_change to a value of true.

Programming Considerations

The switch has several function calls from the reliability module that will need to be either deprecated/removed, or updated.

The recloser and sectionalizer objects are still expected to be sub-classes of the switch. No functional changes are expected to occur with this implementation change, but code updates may be needed to ensure proper functionality.

Testing

Primary testing will be to ensure the switch still passes all existing autotests, particularly those in reliability and those that utilize a switch.

No further autotests should be needed for the base functionality, since the existing autotests already encompass commonly-used scenarios.

See also