Re: [get_losses] Different overall value for active losses

Ray Zimmerman Thu, 13 Dec 2018 11:20:56 -0800

Hi José,

It looks like there are two things that you are missing.

1. The values in the GS and BS columns of the bus matrix are admittances conductance and susceptance values, which correspond to power at 1 p.u. voltages. To get the actual power you must compute it at the solved bus voltage.

2. The branch series losses and line charging reactive injections are handled separately by get_losses(). See help get_losses for details.

Put the attached display_power_balance.m in your MATLAB path and try the following. Here’s what I get …

>> load test_network
>> mpc = loadcase(test_network);
>> mpopt = mpoption('out.bus', 0, 'out.branch', 0, 'verbose', 0);
>> r = runpf(mpc, mpopt);

Converged in 0.01 seconds
================================================================================
|     System Summary     |
================================================================================

How many?   How much?   P (MW)   Q (MVAr)
---------------------   -------------------  -------------  -----------------
Buses     41     Total Gen Capacity   9999.0     -9999.0 to 9999.0
Generators     1     On-line Capacity   9999.0     -9999.0 to 9999.0
Committed Gens     1     Generation (actual)   5.4   -4.3
Loads   7     Load     4.9     0.0
  Fixed   7     Fixed   4.9     0.0
  Dispatchable     0     Dispatchable   -0.0 of -0.0   -0.0
Shunts     9     Shunt (inj)     -0.1     3.6
Branches   41     Losses (I^2 * Z)     0.39   1.56
Transformers     8     Branch Charging (inj)     -   2.3
Inter-ties     0     Total Inter-tie Flow     0.0     0.0
Areas   1

  Minimum   Maximum
-------------------------  --------------------------------
Voltage Magnitude   0.893 p.u. @ bus 18     1.098 p.u. @ bus 3
Voltage Angle   -4.61 deg   @ bus 18     1.46 deg   @ bus 17
P Losses (I^2*R)     -   0.13 MW   @ line 17-27
Q Losses (I^2*X)     -   0.43 MVAr  @ line 14-12
>> display_power_balance(r)

Active Power
Generation   (Pg)   =  5.366418
Load   (Pd)   =  4.882000
Shunt Inj     (Psh)   = -0.094979
Branch Loss     (Ploss) =  0.389439

Reactive Power
Generation   (Qg)   = -4.312679
Load   (Qd)   =  0.036000
Shunt Inj     (Qsh)   =  3.640204
Branch Loss     (Qloss) =  1.559847
Branch Charging (Qchg)  =  2.268322

Active Power Mismatch,     | Pg - Pd + Psh - Ploss |   = 0.000000
Reactive Power Mismatch,   | Qg - Qd + Qsh - Qloss + Qchg | = 0.000000
Individual Branch Balance, max(| Sf + St + Schg - Sloss |)  = 0.000000

Everything is consistent. Feel free to look at how I’m computing things “by hand” in the attached function.

Hope this clears everything up for you,

Ray

display_power_balance.m
Description: Binary data

On Dec 11, 2018, at 4:20 AM, José Paulos <[email protected]> wrote:

Hi Ray, thanks for your input, however, the question remains unaddressed. We are not seeing only the system summary as the values are rounded. We must compare those values with the ones found "by hand" via branches and buses. We have some questions below.

Using the formula you described, and based only on the system summary report, everything goes well:
Active       | Generation + Shunt_Inj = Loads + Losses                       | 5.4 – 0.1            = 4.900 + 0.39
Reactive   | Generation + Shunt_Inj + Transf_Inj = Loads + Losses | -4.3 + 3.6 + 2.3 = 0.036 + 1.56
(reactive load added by hand - the summary was rounding it to 0)
<hnfiliohnncccphc.png>
However, when analyzing it "by hand" via powerflow.bus, we are not understanding the differences:
get_losses gives us the active and reactive losses via

Active Losses sum(abs(real(losses))) 0.3894

sum(real(losses)) 0.3894

Reactive Losses sum(abs(imag(losses))) 1.5598

sum(imag(losses)) 1.5598

powerflow.gen gives us the Generation (both Active and Reactive)
powerflow.bus gives us the Loads and Shunts

Active Generation powerflow.gen(1,2) 5.3664

Reactive Generation powerflow.gen(1,3) -4.3127

Active Shunts sum(powerflow.bus(:,5)) 0.0865

Reactive Shunts sum(powerflow.bus(:,6)) 4.3080

Active Loads sum(powerflow.bus(:,3)) 4.8820

Reactive Loads sum(powerflow.bus(:,4)) 0.0360

When comparing this values with the system summary, the shunts values are different, why?

System Summary sum in powerflow.bus

Active Shunts -0.1 0.0865

Reactive Shunts 3.6 4.3080

Active       | Generation + Shunt_Inj = Loads + Losses | 5.3664 + 0.0865 = 4.8820 + Act_Losses | Act_Losses = 0.5709 != 0.3894 (Why?)

Active_Alt | Generation + Shunt_Inj = Loads + Losses | 5.3664 - 0.0865 = 4.8820 + Act_Losses | Act_Losses = 0.3979 != 0.3894
(Why?)
Reactive   | Generation + Shunt_Inj + Transf_Inj = Loads + Losses | -4.3127 + 4.3080 + ? = 0.0360 + React_Losses | Is it possible to check the Transf_Inj Manually?
---------------
Also, when summing the branches PF/PT and QF/QT, the results are inconsistent:
PF+PT = sum(powerflow.branch(:,14))+sum(powerflow.branch(:,16)) = 0.3894 = active_losses_by_get_losses
QF+QT = sum(powerflow.branch(:,15))+sum(powerflow.branch(:,17)) = -0.7085 != reactive_losses_by_get_losses

José Paulos
Centro de Sistemas de Energia
Centre for Power and Energy Systems

INESC TEC
Campus da FEUP
Rua Dr Roberto Frias
4200-465 Porto
Portugal

T +351 91 424 1519
F +351 22 209 4050
[email protected]
www.inesctec.pt

On 10-Dec-18 17:04, Ray Zimmerman wrote:

The shunts are not included in the loss numbers, so everything does add up.

Generation = 5.4 MW

Loads = 4.9 MW

Losses = 0.4 MW

Shunt Inj = –0.1 MW

Generation + Shunt Inj = Loads + Losses

5.4 – 0.1 = 4.9 + 0.4

Ray

On Nov 29, 2018, at 10:06 AM, José Paulos <[email protected]> wrote:

Hi Ray, thanks for your input.

In fact, we weren't considering that. However:
When analyzing the case_info we get:

Shunt Injections
    active (MW)            -0.1
    reactive (MVAr)         3.6

I'm assuming that those are simplified values, but in our network, we have:
Sum of the GS Shunt Conductances = 0.0865 MW
Difference between calculated losses vs. get_losses = 0.095 MW (that were supposedly due to the missing GS values)
Resulting a difference of 0.0085 MW (even this is different from the -0.1 MW active shunt injections).

José Paulos
Centro de Sistemas de Energia
Centre for Power and Energy Systems

INESC TEC
Campus da FEUP
Rua Dr Roberto Frias
4200-465 Porto
Portugal

T +351 91 424 1519
F +351 22 209 4050
[email protected]
www.inesctec.pt

On 27-Nov-18 20:03, Ray Zimmerman wrote:

You are missing contribution of the shunt elements defined in the GS and BS columns of the bus matrix. These also contribute to the overall power balance. Have a look at …

case_info(powerflow)

… after running your test_file.

Ray

On Nov 27, 2018, at 11:53 AM, José Paulos <[email protected]> wrote:

Hi,

We have a network with the following configuration:

%% system MVA base
mpc.baseMVA = 100;

%% system voltage levels (kV)
mpc.V_levels = [
    0.4    15.0    30.0    60.0
];

%% system summary
% number of buses:             41 (1 REF | 1 PV)
% number of branches:       41 (8 transformers)
% number of loads:            21 (including Pd/Qd = 0)
% number of generators:    2
% number of capacitors:     2

We use get_lossses, in this case:

    %%% compute the losses
    losses = get_losses(powerflow);
    %%% the active losses
    active_losses = sum(abs(real(losses)));

The balance between the injected active power and the Loads/Gen's is not equal to the result of the get_lossses procedure described.

Follows attached the case (run test_file.m with test_network.mat in the same dir)
Thanks in advance,

--

José Paulos
Centro de Sistemas de Energia
Centre for Power and Energy Systems

INESC TEC
Campus da FEUP
Rua Dr Roberto Frias
4200-465 Porto
Portugal

T +351 91 424 1519
F +351 22 209 4050
[email protected]
www.inesctec.pt

<test_file.m><test_network.mat>

Re: [get_losses] Different overall value for active losses

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