Analele Universit ății din Oradea Fascicula de Energetic ă, Vol. 15 2009 [600221]

Analele Universit ății din Oradea Fascicula de Energetic ă, Vol. 15 2009

THE POWER ELECTRIC AUDIT OF AN
URBAN TRANSPORT OPERATOR

Ioan FELEA, Mihnea CÂMPAN, Florin DAN
University of Oradea, Universit ății no.1, Oradea,
[anonimizat]

Abstract – The paper is structured in four parts. In the first part we justify our concern regarding the
power audit. In the second part we define the contours
and how to work making AEE for an operator of
urban transport. Part three contains a summary of the
results, and the last part presents the conclusions of
the analysis.

Key words – power electric audit, power efficiency,
urban transporta tion
, power optimization

1. INTRODUCTION

Sustainable development is one of the dominant
themes of globalizatio n
. Operation of this concept, in the
energy field is seen, mainly by reducing fossil fuel in two
ways:
• By increasing the energy ef ficiency of processes;
• By increasing the value of renewa ble e
nergy.
Targets and means of action of the European Union
are clearly defined a nd regulated [8.9] aimed, in essence,
by 20 2
0, reducing energy consumption of fossil fuels by
20% and corresponding increase in the share of
renewable.
In Romania, energy efficien cy is well below th at of
countries with th
e technology. There are still many
processes and services that take place in Romania's energy intensity of [2-3] times higher than similar
processes in countries modernized "flag" as
technologically. In the last period to make legislative and
financial efforts [10.11] to align the state of facts of
Romania to the European standards, both in terms of energy efficiency and in te rms of more intense use of
renewable resources.
Audit of power (AP) is one of the ways covered [12]
to identify
ways of improving efficiency of processes of
energy conversion. EEA conducted an operator of urban transport – SC URBIS S.A. Baia-Mare. After specifying
the elements that define th e contour and some specific
aspects of mathematical modeling, there is given the conclusions of the made study with general interest, taking into account, the weight of the power traction of
Romania and the possibilities to increased the efficiency.

2. CONTOUR AND THE WORKING METHOD

The AP contour of the electric urban transport Baia
Mare, comprising o
ff: • transformer stations and rectifier:
Station S1:
Trafo type TTUONAN; 2X1500 kVA (passive
reser ve) 20 / 0.
511 kV
Rectifier type RSTU 825/1600-231B1
Own service trafo 40kVA, 20 / 0,4 kV
Station S2: Trafo type TTUONAN; 2X1600 kVA (passive
reser ve) 20 / 0.
511 kV
Rectifier and own services trafo the same type as
in S1 .
• Sup
plying Network (injection and contact):
Injection network (RI): 7 segments [150 ÷ 2600]
ml long of A C
YEY 300mmp cable, length 5180
ml;
Network contact (RC): operates at 600 Vcc,
sections 7, 9200 m
l (about double), conductor type
TTb 80
• The trolley buses fleet, consist currently of 3 types of
trolley buses:
SAURER GT 56
0/640-25 – (7 pcs), 148 seats,
driving asy n
chronous motor fed by inverter
ROCAR EDM 212 E – (3 pcs), 92 seats, driv en by
DC motor (classic)
ROCAR EDM 217 E – (1 pc), 156 seats, driven
by
DC motor (classic)
AP was done in accordance with [12].
Based on measurements and characteristics of
equipment an d
facilities in contour, the real power
balance (PB) has been operated, and identifying measures to reduce energy losses, has been developed optimized
PB.
The documentation also includes evaluation of energy
efficiency of energy c onsum ption p rocesses
, the
calculation of economic efficien cy for the main measures
for optimization assessment elements and environmental
impact.
The extent of the service performed is pl ayed by
specific indicators: tours nu mber (CN), distance (D),
passenger transported (NCL). In October 2008 the value of these indicators was:
N
c = 2552;
D = 38.280 km; N
CL = 502.030 passengers;
The average of the indicators listed for a day are:
Nc = 82 tours/day;
d = 1234.84 km/day; n
cl = 16.195 passengers/day;
The reference unit associated PB is one classic work
day (24 h
ours), average. Electricity consumption for an
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Analele Universit ății din Oradea Fascicula de Energetic ă, Vol. 15 2009
average day was determined from the records kept in the
• [22.11.2008, at 15:30 ÷ 29.11.2008, at 15:30] station
S1-
• [22.11.2008, at 17:00 ÷ 29.11.2008, at 17:00] station
S2-
The loading of equipment and plant during the
devel opment of the m easurements were norm al for the
service p
rovided by SC URBIS SA Baia Mare. After the
development of the BEE for an average day we will refer
to the annual BEE, based on monthly records of EE.
Devices used so far:
• network analy
zer (NA) type C.A. 8334 B (2pics.),
located in the secondary of
the two transformers;
• The keyboard devices indicators of stations S1 and S2;
→ magnetoelectric voltmeter: [750-0-750] V;
→ magnetoelectric ampermeter [1300A/75 mA]
• meters for active and reactive power: Type
ENERLUX TCDM-AEM Timi soara, accuracy class
0.5, located i n
the primar y of the transformers.
For example, is presented in fig.1 load curves (P, Q,
S) of the S1 stat i
on, during recording, and in Fig.2 load
curves (P, S) of the station S2, for a day of transition.

Fig. 1 – The load curve for analyzed interval
(station S1)

Fig. 2 – Load curve for the analysis period
(station S2)
The values of THD indicators are:
• For S1station:
THD
U = 2402%% THD I = 23038;
• For S 2 station:
THD U = 1554%% THD I = 21711;

For the above evoked level of deforming residue
it’s ju stified the evaluation of p
ower losses / energy
in the two winding of the power transformers.
Through aggregation and mediation during the
analysis of recorded values for the recorded technical
measures, were obtained the values characteristic of
the average day, used to assess energy losses. In
accordance with the requests of the beneficiary, the BEE has been carried out on the following subcontour :

SC1 – Transformation Station – rectifier and supply
network , for which we have used
the following equation
of PB:

Wa = W U + ΔWT +ΔWR + ΔWL + W A (1)

where, W
a – input power, measured at the inlet (separation) of the
station with SEN (determined from records of the beneficiary);
W
U- useful energy (leaving subcontour), conveyed to the
allocated trolley buses;
ΔWT – energy losses on transformers in the rectifying
station based on measurements of the technical
configuration and operation of the station in question;
ΔWR – energy losses on the rec tifiers from the rectifying
station, based on measurements of the technical
configuration and operation of the station;
ΔWL – energy losses on the su pply calculated on the basis
of measurements and features sections (TI, TC), have two
components:
→ ΔWLI energy-losses on the injection network;
→ ΔWTC energy-losses on the contacts network;
→ WA- the auxiliary input powe r in station (the station's
own serv i
ces)
Value size Δ WT, ΔWR, ΔWL is determined by
calculation based on records kept. The value of the auxiliary consumption (W
A) is calculated as follows:

WA = W a-W aJT-ΔWT (2)
W
aJT- input power / recorded on low voltage (recordings
made by AR);
Evaluations are made for average day. Energy use is
determined by calculating th e relatio
nship (1). We
calculate the additional losses in power transformers due
to deforming operation mode [16].

SC2 – trolleybuses , wh ich for was u sed th e following
equation BEE

Wa = W U+ΔWM+ΔWmec+ΔWA (3)

where, W
a – input power is calculated based on the results of
previous sub contour;
ΔWM – energy losses in engines of the trolley bus,
based on the efficiency an d degree of loading (simple
model); ΔW
mec – energy losses calculate d from the records in
no-loads (at the start in the parking stations); ΔW
A-expected energy losses in other parts of the
trolley bus, based on records in the task and no-loads
based on its technical characteristics;

Based on equation (3) calculating energy use (W U),
representing the consumed energy for passengers transport. It will be compared the obtained values with the
values from technical card of the trolley bus. Will be
make comparisons between the 3 types of trolley buses.
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Analele Universit ății din Oradea Fascicula de Energetic ă, Vol. 15 2009
3. RESULTS

In fig.3 and 4 are presented charts of real BEE for SC1
(S1, S2)

Fig. 3 – BEE real SC1 (S1)

Fig. 4 – BEE real SC1 (S2)

To determine the power function of the trolley bus in
no-loads (P 0) was started in conjunction with chart
records of the two AR [7]. Were obtained the power components listed in Table 1.

Table 1 – The power components of the PB for
trolleybuses
Tip/Comp
Power[kW ] S-GT 56
0 ROCAR 212 E ROCAR 217 E
Pa 64,94 42,6 49,85
Po 25,33 16,73 22,71
ΔPM 5,84 7,67 10,97
ΔPA 3,71 1,51 2,25
ΔPmec 15,78 7,55 9,48
ΔPu 39,61 25,87 27,15
η[%] 61 60,7 54,5

Real PB of 11 trolley buses (SC2), with reference to
average day records appropria te on av er
age records for
many months are given in Table 2.
Table 2 – BEE real for SC2
Feature size [kWh] [%]
Input power [W a] 2556,105 100
Output power 2556,105 100
1. Useful Energy [WU] 1545,305 60,46
2. Losses 1010,8 39,54
• engines [Δ WM] 302,43 11,83
• other electrical
components [Δ WA] 132,31 5,18
• mechanical transmission
mechanisms in [ ΔWmec] 576,06 22,53

For fixed contour of real BEE we obtain by adding
components and havin g
in mind that energy useful for the
two under contour of the two substations (S1, S2) is the energy absorbed by the 11 trolley buses. The results are
shown in Figure 5.

Fig. 5 – Sankey Diagram of real PB for
the analyzed contou r

Indicator
s of energy efficiency that is suitable to b e
calculated [12]: • specific energy consumption for the unit
→ consumption of power for a tour:

Cc=Wa/Nc=127090/2552=49,8 kWh/tour (4)
→ EE specific consumption per unit of length traveled

CD = Wa / D = 127090/38030 = 3.7 kWh / km (5)
→ specific consumption of EE per passenger transported

CCL=Wa/NCL=127090/502030=0.25kWh/passenger (6)

Allowing an average weight for a passe nger (75
kg) is
finding that loading to maximum can be calculated on the
specific "t km":

CCD = 127090 / (38280km 25t) = 0,1328 kWh / (t km)
Considering the price of a journey (1,3 lei) and the
cost EE (0,315 lei / kWh) it can be calcu
lated:

• Value of EE cost for unit "km t”'
Ven/z = (127090 0,315)/(38280 25)=0,042 lei/t km
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Analele Universit ății din Oradea Fascicula de Energetic ă, Vol. 15 2009
• Income on "kWh" consumed

Ven = (1,3 502,030)/127090=5,14 euro/kWh.
Point out that the evaluatio n of e nergy efficiency
indicato r
s has been based on
data from October 2008.
Environmental impact is evaluated by determining the
quantity of pollut an
ts discharged into the atmosphere [12]:

E = B · Qi· ε (7)
B-Amount of fuel consumed in the analysis (one day)
[kg];
Qi-calorific power of the fu el
[kJ / kg];
ε – emission factor
We will assess the impact of admitting that the energy
consumed in S.C. URBIS Baia Mare is p r
oduced from the
lignite having calorific value:

Qi = 1700 kJ / kg = 0.47 kWh / kg

The results are shown in Table 3:

Table 3 – Quantities of po llutants e xpected to be
emanate d (o
n average day, multi- yearly)
The energy component Pollutan
ts [kg] Cons.
ener Loss of ener.
cons. in recov
stations a
nd
feed networks Loss of
ener. in
the
trans .
SO2 153,6 53,5 39,57
NOx 2,84 0,99 0,73
CO2 1390,8 484,7 358,3

4. CONCLUSIONS. OPTIMUM BALANCE

Measurements and assessments made in the audit
(AP) of the contour established b y
S.C. URBIS Baia Mare
– the electric urban transport, composed of transformers –
rectifier stations (S1, S2), the supply (injection and contact) and trolleybus park – allow formulating the
following conclusions:
4.1. The energy efficiency of equipment and contour of the
structure it falls within th e
normal limits for such systems.
4.2. Power transformers and rectifying stations (S1, S2) is
well below t h
e rated output. Thus the apparent maximum
load recorded during interval in which the records with
the network analyzer is
326.2 kVA – for station S1, with the power transformer
rated 1500 kVA;
22
0.7 kVA – for station S2, with nominal power 1600 kVA
The average value of relative loading (β ) is well below
optimal rela tiv
e loading ( β0) of power transformers, as
follows:
For trafo of station S1: βm = 0.081 and β 0 = 0.64, so S 0 =
960 kVA
For trafo of station S2: βm = 0.041 and β 0 = 0.54, so S 0 =
864 kVA
For rectifiers this under load regime of this arrangement is
beneficial both i n
terms of ener gy efficiency as well as in
terms of reliability.
For transformers, the under load regime implies energetic inefficiency under th e energy
issue, which is reflected in
chart of balance of powers, on the contours of analysis,
energy losses in transformers is 6.16% of energy came in
contour.
4.3. The two stations (S1, S2) have a pronounced
imbalance in term s o
f load. Thus the station S1 is
circulating about 63% of the load, while the station S2 only 37%.
4.4. Supplying Network (injection and contact) and
sections of the st
ructure have a high load imbalance, both
between the two sources (S1, S2) and between sections,
where the range of variation is between 3% (section 6)
and 27% (section 1) of the total load. All injection
sections are under loaded, which is beneficial for the
reliability and energy efficiency of them.
Changes in the degree of loading stations and sections of
the supplying netwo r
k reflects certain structure charts and
routes of transport, by the beneficiary based on the
necessity of community and economic efficiency for
transport operator.
4.5. Electrical load value (cu rrent, po we r) is highly
variable, specific to the driving power of vehicles. This is
inevitable and it’s reflected by the increase losses in
transformers and power network supplying, compared to the case that the load would be constant.
4.6. Consumption of power (energy) is below the reactive
appropriate neutral power factor, whic h im plies an
absence of rea ctive
energy bills.
4.7. The voltage harmonics in accordance with the rules
(THD U = 2.4% -station S1; THD U = 1.55% – station S2).
Harmonic current level is well above the limit indicated in
the normative (
THD I = 23% -station S1; THD I = 21.7% –
station S2). These values of the current harmonics reflect the poor sizing or downtime of the filter in the recovery
power of the two stations. The power effects of the current harmonics (additional energy losses) are
negligible due to the low lo ading of the transformers.
4.8. Auxiliary power consumption in power stations (S1,
S2), of its
own services (technological own consumption)
is too high (22.83%) compared with normal values [(10-
12) %]. Value of Auxiliary (WA) was determined based
on measurements concomitant – with its own meter and
network analyzer – in station S1.
4.9. Measurements and assessments made with reference
to the 3 types o f
trolley buses, reflects the existence of
values close to the "efficiency" ( η) for two types as
follows:
61% – trolley bus Saurer 560 GT;
60.7% – 212 E. ROCAR trolley bus
A less sensitive (54.5%) was obtained for a trolley bus ROCAR 2 17 E.
4.10. For all of th
e 11 trolley buses from measurements
and assessments ma de, con
sidering trolley buses
equivalent of the same type, it obtains a good yield (60.46%) and show that energy losses occur, mainly in the mechanisms of transm ission (22.53%) and engine
(11.83%).
4.11. Based on records from October 2008, it shows that
the average nu m
ber of passengers transported is 196,
which exceeds the amount recommended for
the transport capacity of each trolley. Therefore, the 11
are load e
d at the maximum.
4.12. The value calculated for the specific energy
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Analele Universit ății din Oradea Fascicula de Energetic ă, Vol. 15 2009
consumption on” t km “determined based on AP is 132.8
Wh / t km. This value is below the value specified in the
technical card of trolley bus type ROCAR 212 E (160Wh
/ t km – at nominal load).
This finding reflects a trolleybuses operation at a normal
level of energy efficiency.
4.13. For the entire c ont
our, en ergy effici ency is a bout
39.4%, the larger energy leak it is located in the under
contour of the supplying network and recovery stations
(34.85%) and not in the vehicles (25.76%). This unusual state is determined by excessive auxiliary consumption of
the recovery stations (22.83%).
4.14. Reducing energy consum ption in the analyzed
outlines can b e
done by applying the following technical-
management measures:
a) Replacement of the under lo aded transformers with
trans fo
rmers adapted to the consumption;
b) balancing the electric power networks (injection and
contact);
c) replacing less efficient trolley bus (ROCAR EDM 217
E) with a perfor m
ance one like (Saurer GT 560);
d) reduction of the consumption in the auxiliary rectifying
stations.
Measure b) is nonrealistic and
is there fo re not taken into
account in preparing th e optimal balance.
We further analyze the eff ect of other measures.
a) The existing power transformers can be replaced with
400 kV
A transform e
rs, appropriate to the loading level. By
this measure we would achieve 50% reduction in loss of
power transformers that is an economy of 120,838 kWh/day, respectively 1058,541 MWh / year. This
measure is also economically feasible.
c) By replacing ROCAR EDM 217 trolley bus with a
trolley t
ype Saurer GT 560 we obtain increased efficiency
of the transport system (the 11 trolley buses) from 60.46%
to 60.9% and a saving of about 4,45 kWh / day, or 38,982
MWh / year.
This is feasible if the trolley bus ROCAR 217 E is
towards the en
d of the period of useful life.
d) reduction of auxiliary stations recovery from 22,83%
to 12,83% lead to a sub s
tantial energy savings, namely:
392,345 kWh/day, respectively, 3436,942 MWh / year.
4.15. By applying the m ea sures written above, if the
evoked results are obtain, we will have a PB optimum
(fig.6)

Fig. 6 – Sankey diagram of optimal PB
for the analysed contour
4.16. By applying specific m easures to achieve optimal PB
we reduce the impact on the environment by reducing the
quantities of pollutants discharg ed in the atmosphere [7].

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