1. University of Padua
DEGREE DISSERTATION
29° February 2008
Electrical Energy Accumulation System
For Ropeways
RELATER: Prof. Andrea Tortella
CORELATER: Ing. Leonardo Sartori
GRADUATED: Rigoni Garola Filippo

2. RopewaysRopeways
1. On monocable ropeways the function
of carrying and hauling the vehicles is
taken over by just one rope, the
“carrying-hauling” rope. Generally
these types are used on short path with
high loads.
 Fixed grip
 Detachable grip
2. On bicable ropeways there are one (ore more)
carrying rope which the vehicle rolls by means
of its carriage, and one (ore more) hauling
ropes that propel the vehicles.

Continuous cycle

Jig – back or reversible cycle

3. Jig – Back RopewaysJig – Back Ropeways

4. If a jig-back ropeways has more then one pylon, the applied force on the hauling rope
(vector sum of the forces applied on the vehicle ) is irregular.
Such kind of force generate an irregular
resultant diagram that obviously caused an
irregular electrical load diagram.
This irregularity is not appreciated above all
with low voltage power supply and with low
short circuit power.
Jig – Back RopewaysJig – Back Ropeways

5. Accumulation systems
applications
Thanks to the installation of a
properly electrical accumulation
system there is the possibility of
load diagram regulation that
ensures the following
advantages:
1. An increase of the electrical
in coming power line quality;
2- cost effective solution in
terms of electrical power
savings;
3- a resizing of the entire
accumulation upstream
system;
4- an increase of the global
electrical system
performances.

6. Types of accumulation systemTypes of accumulation system
1. Multiple conversion
 Electrochemical cells
 Inertial system
 Potential system
2. Single conversion
 Superconductive system
(S.M.E.S.)‫‏‬
 Super capacitors system
The first family is composed by all the systems in which conversions between
electrical and a more adaptable accumulation energy, and vice versa, are
subsequent.
Beside in the second family there are all the systems in which there is only one
conversion that uses the energy correlated to the electrical one:
• magnetic energy,
• electrostatic energy,
The traditional transducer: resistance, inductance and capacity are related to
their specific energy conversion. Besides for the magnetic and electrostatic
energy there are well known transducers. Single conversion systems have a
very low specific accumulation energy with the tradition transducers. This is the
main reason to choose multiple conversion systems.

7. 1.1 Electrochemical cells1.1 Electrochemical cells

Lead-acid cells, lead-gel;

Nickel cells:
 Ni-Cd
 Ni-Mh
 Ni-Zn
 Ni-NaCl

Lithium cells;

Na-S cells;

Fuel cells.

ADVANTAGES
 Well known technology,
 reliability,

DISADVANTAGES
 emission of dangerous gases,
 high maintenance,
 short working life,
 Low specific features,

8. The inertial systems use the kinetic energy accumulation. Their key points are the high
accumulation capacity and the longevity. Besides their cost is higher due to an higher
need of volume and precision realizations. Moreover the high working life caused more
cost for maintenance; necessary because there are parts moving with high speed that
need cycle security measures.
ADVANTAGES

Good specific features,

High reliability,
DISADVANTAGES

High noise,

Possible risks of violence
broken,

reduced responsiveness
1.2 Inertial system1.2 Inertial system

9. This system use the potential energy accumulation, especially the gravitational one.
The system is based on the recovery of geodetic energy, created by a mechanical
energy applied to a body scaled to a certain height. The electrical motor is normally
used, in this kind of solution, to generate the mechanical energy.
HYDROELECTRIC: facilities where the
electrical energy is absorbed during the
working gaps and gave back during the
peaks.
C.A.E.S. (compressed air energy
sorage): facilities where the air is
compressed into natural or special
cavity.
Usually combined to a Bryton cycle to
recover the heat, generated during the
compression, to produce a
cogeneration.
1.3 Potential system1.3 Potential system

10. Superconducting Magnetic Energy Storage (SMES) systems store energy in the
magnetic field created by the flow of direct current in a superconducting coil which has
been cryogenically cooled to a temperature below its superconducting critical
temperature. A typical SMES system includes three parts: superconducting coil, power
conditioning system and cryogenically cooled refrigerator. Once the superconducting
coil is charged, the current will not decay and the magnetic energy can be stored
indefinitely.
ADVANTAGES:

high specific energy,

reduced response time.
DISADVANTAGES:

high realization and maintenance costs,

hazardous materials used (hydrogen);

maintaining the structure at low temperatures;

need for special and expensive facilities .
2.1 Superconductor system2.1 Superconductor system

11. The super capacitor systems are characterized by an high
load and specific capacity. They are made by standard
electrolytic capacitor features armors fitted with a porous
carbon sink or trough micro carbon tubular structures.
This specific solution can ensure from 1000 up to 3000
square meters per gram.
ADVANTAGES:

Maintenance absence,

Moving parts absence,

High temperature range,

High performances,

High specific power,

High reactivity,
DISADVANTAGES:

Cells tension reduced,

Low specific energy,
2.2 Super capacitor system2.2 Super capacitor system

12. Accumulation system comparisonAccumulation system comparison

performance,

working life,

reaction time,

costs,

specific parameters
Comparison
parameters:
The best accumulation system is the one that uses more independent equipments
that cooperate together to reach the same goal, so to have the more efficient
solution for the specific application.

13. The design of a proper system of accumulation, able to regulate the electrical load,
starts from the definition of the electrical diagram as the resultant of the strengths on
the carrying rope.
There is the possibility to determinate the
motor and bus DC power, necessary to
define the energy value for the accumulation
system , if is known the speed trend.
Accumulation system on jig – back ropewaysAccumulation system on jig – back ropeways
Load uphill – Empty downhill (including masses winch)
Speed
Nominal engine power
Average square engine power

14. POWER OPTIMIZATION: the optimum power is defined as the one needed for the
network that is the right technical and economical compromise considering the
balance of additional charges and savings generated.
The accumulation system will supply the
additional power, to the optimized one,
need from the totally carrying plant.
Sizing of the accumulation systemSizing of the accumulation system
Instantaneous power
Optimized power
Average power

If the optimized power is higher then the
average power, its network permanence
will be lower then the cycle time;

If the optimized power is lower then the
average one its network permanence
will be higher then one rope loop;

If the two powers will be the same its
network permanence will be as the cycle
time unless losses.

15. TECHNOLOGY CHOOSE :
1. Low maintenance;
2. High reliability;
3. Low weight and small spaces;
4. Low rumors and vibrations;
5. High working life in terms of upload and download cycle numbers and
performances;
6. High capacity of features maintenance in presence of environment changes,
above all temperature and pressure;
7. No danger to humans and environment, not explosion dangerous, fire and toxic or
dangerous emissions and pollution in general;
8. High response rapidity, even after long periods of stop.
All these considerations bring to the super capacitor system choice
but does not rule out the possibility of a flywheels cooperating
system increasing the value of specific energy.
The idea of using SMES systems is immediately rejected, because
in periods of half-season the plant would be stopped and those
would caused strong technical complications.
Sizing of the accumulation systemSizing of the accumulation system

16. DETERMINATION OF ENERGY MANAGED BY ACCUMULATION SYSTEM:
This is actually represented from the peak curve of power area that the condenser
should provide on the conditions provided.
The peak power diagram is obtain by subtracting from the optimized power the bus DC
curve. Its area can be calculated trough numerical methods, however the geometric
method should be easier thanks to the curve shape, this involves a lesser effort in the
calculation.
Sizing of the accumulation systemSizing of the accumulation system
Instantaneous power
Optimized power
Average power

17. CAPACITY CHOSSE :
1. Should be considered the manner in which the SC gives energy to the load;
2. Energy should be calculated in addition to the losses dissipated in the SC;
3. Should be considered that the SC has a capacity that is a linear function of the
voltage applied to the heads;
4. Should be considered the minimum voltage of SC determined by their current limit
and a possible converter applied.
To calculate the value indicative of capacity
it start from considering the maximum and
minimum limits of tension that the whole SC
system can reach. It then assumes the
lower starting capacity the previously one
calculated. It determines the performance of
the SC voltage corresponding to the loading
diagram. It calculates the value of proper
capacity that imposing the minimum of
tension coincides with the minimum
expected.
Sizing of the accumulation systemSizing of the accumulation system

18. CAPACITY DETERMINATION
The capacity should now be increased taking into account the points 2 and 3 in the
previous sheet. In fact the energy that the SC should contain has to consider the
losses the linear dependence of capacity despite the tension.
The value of final capacity will be:
Wpik is the calculated energy starting from the peak curve area by imposing the
minimum voltage;
Wj is the energy lost due to various effects (mainly thermal);
k is a factor which takes into account the dependence of the capacity from the
voltage
Vmax Vmin and are calculated taking into account the component limitations
(current maximum allowable) and the limitations of the converter applied.
Sizing of the accumulation systemSizing of the accumulation system

19. The first solution shows that the
tension of the SC is bounded by the
limits imposed by the converters and
carrying line. This implies an
expensive design capacity. The range
of variability of tension, in this case,
goes from 620 V up to 750 V.
The second solution, seemingly less
convenient, would provide a much wider
variability in the tension of SC thus enabling
capacity values sharply lower. The cost of
additional converter is offset by a reduced
burden on the SC. This solution is adopted in
the period under investigation and allows a
voltage range from 360 V up to 750 V.
Electrical equipment architectureElectrical equipment architecture
1
2

20. To validate the theory to practice
has been done a simple test that
includes the use of:
The test aims not only to verify the
reliability of the sizing calculation model,
but also wants to verify certain parameters
stated by the manufacturer. A great
importance is the estimation of
performance that has shown excellent
results with values higher than 90%.
Load Power
Capacitor Power
Power supply
Vdc Tension
Super capacitor testsSuper capacitor tests

a power supply stabilized and
current limited,

a rheostat load,

a super capacitor

a series of measurement
systems.

21. Diagrams for the first and second parts of
the system, required for the DC bus, are
reported in the two figures in side. It is
shown that the maximum power has been
almost halved.
ConclusionConclusion

The system of accumulation can
provide service continuity even in
temporary absence of power supply,
without the help of generators;

The sizing of generators is less
expensive because it is based, rather
than on peak power, but on the
"optimal" one;

The use of accumulation systems
ensures a better use of the energy
required by the network minimizing the
value of losses.
In particular for a rope way the system of
accumulation does not involve only the
advantages cited at the beginning, but
allows other advantages:

22. ConclusionConclusion
Data Part 1 Part 2 Dimension
Peak power 365 390 kW
Optimal power on critical part (maximum climb load) 220 200 kW
Total critical part energy 12,6 16,6 kWh
Accumulation system energy 2,14 3,18 kWh
Capacitor voltage limit 750-360 750-360 V
Bus DC voltage 750 750 V
Calculated capacity 35,7 50,2 F
Optimized module BMOD0018-390V BMOD0018-390V V
Number of module 8 12
Number of serial module 2 2
Number of parallel module 4 6
Effective capacity 36 54 F
Indicative capacitors cost 134000 200000 euro
Convenient module BMOD0094-75V BMOD0165-48,6V
Number of module 40 80
Number of serial module 10 16
Number of parallel module 4 5
Effective capacity 37,6 51,5 F
Indicative capacitors cost 123000 165000 euro